Advertisement

High-resolution molecular stratigraphy of Oligocene–Miocene sequence of Tumaco-1-ST-P well, Tumaco forearc Basin, Colombia

  • J. E. CortesEmail author
  • A. Mejía-Molina
  • C. A. Vargas
  • S. I. Cortes
Open Access
Original Paper - Exploration Geology
  • 66 Downloads

Abstract

In the present work, high-resolution molecular stratigraphy technique has been applied to the rock samples from Tumaco-1-ST-P well to investigate vertical variations of the deposited organic matter (O.M.) based on screening parameter and high-resolution biomarkers in both saturate and aromatic fractions in order to establish its origin, organic facies, depositional paleoenvironment, thermal maturity, biodegradation processes and to evaluate the exploratory potential in this frontier forearc basin. The O.M. is immature with a high concentration of biolipids (early diagenesis) and with poor to fair generation potential originated from a type II/III or III kerogen. Original total organic carbon (TOCo) and original hydrocarbon index (HIo) values for each formation and lithology are determined to evaluate the hydrocarbons potential in the basin. n-alkanes, isoprenoids, and tricyclic terpanes suggest an algal/bacterial and terrestrial input deposited on a marine-deltaic shale under oxic to suboxic conditions. The O.M. was deposited on siliciclastic rocks in a marine-continental (transitional) environment, although carbonate rocks were also deposited in the bottom of the column (late Oligocene). The molecular stratigraphic interpretation allows to conclude that organic facies and lithology in Tumaco-1-ST-P are characterized in Cascajal and Tangareal del Mira Fms. (1000–5000 ft) by a marine-deltaic paleoenvironment with an important terrestrial contribution and varying between deltaic plain and prodelta during the late Miocene. At the top of Tumaco Fm (5000–9000 ft) in the late to medium Miocene, the depositional environment was like the marine delta of the Tangareal del Mira Fm, changing to a marine platform environment at 8000 to 10,000 ft depth in the middle to early Miocene. Toward the bottom of the column (10,000–12,000 ft), Tumaco Fm was deposited in the late Oligocene under a marine shelf environment. In the present paper, we propose a modeling approach, based on the evolution of the thermal maturity through the stratigraphic column, that at 17,000 feet depth could exist rocks with O.M. in the hydrocarbon generation window for Tumaco Basin, Colombia.

Keywords

Hydrocarbon source rock Marine-deltaic environment Thermal maturity Saturate–aromatic biomarkers Frontier basin Tumaco forearc basin 

Introduction

Tumaco basin is a frontier basin under the influence of a subduction zone of the Pacific active margin. Consequently, the importance of both the new stratigraphic and the geochemical data is essential to provide new information for developing new exploration projects in the Colombian Pacific margin. The Tumaco-1-ST-P stratigraphic well gives evidences of the Tumaco basin sedimentation system during the late Oligocene to Pliocene, dominated by the movements of the paleodeltas of the Tumaco and Mira rivers (ANH-Universidad de Caldas 2011, ANH-Antek S.A. 2013). In the late Oligocene-middle Miocene, Tumaco Fm is observed the presence of a large deltaic complex (associated with paleodelta of the Patia River), with sources areas that involve, at least partially, the Central Cordillera. For the late Miocene–early Pliocene, the displacement to the north of the Patía River leads to the establishment of the Mira fluvio-deltaic system in the area, represented by deposits of the Tangareal del Mira Fm, which is the only present source areas of the Western Cordillera. Finally, in the late Pliocene, deltaic deposits of Cascajal Fm record a period of intense volcanism (ANH-Antek S.A. 2013).

The application of high-resolution organic geochemical techniques to evaluate the sedimentary sequence on a “layer-by-layer” basis is called “molecular stratigraphy” (Brassell et al. 1986; Farrimond et al. 1990; Keely et al. 1993). In this study, this approach was applied to investigate the evolution of the sedimentary organic matter in the Tumaco-1-ST-P stratigraphic well in the range between 750 and 11,930 ft covering the Miocene–Oligocene sequence in the onshore Tumaco basin, Colombia to characterize the origin and type of organic matter, paleodepositional environment, genetic relation between bitumen, maturity, and possible degradation processes in a sedimentary basin under the subduction influence.

Geological setting

Regional stratigraphy

The onshore Tumaco basin is located in the southwestern of Colombia. The basin is bounded by the Garrapatas fault system in the north, Ecuador country in the south, Western Cordillera (uplift) in the east, and the Pacific Ocean in the west (IGAC-Ingeominas 2001; Barrero et al. 2007; Cediel et al. 2010; ANH-Universidad de Caldas 2011; Borrero et al. 2015). The Tumaco forearc basin contains a pre-Miocene mega-sequence and three post-lower Miocene sequences deposited in shelf to bathyal environments. The basin basement is made up of Cretaceous metasedimentary and volcanic rocks (Cediel et al. 2010). The study area map and detailed stratigraphy column of the Tumaco-1-ST-P well are given in Figs. 1 and 2, respectively (ANH-Antek S.A. 2013).
Fig. 1

Map showing the study area and location of the Tumaco-1-ST-P stratigraphic well (ANH-Antek S.A. 2014)

Fig. 2

Generalized lithostratigraphic column of Tumaco basin (ANH-Antek S.A. 2014)

Previous work including a detailed discussion of the geology of the onshore Tumaco basin is found in the literature derived from recent projects led by National Hydrocarbon Agency, Colombia (Universidad de Caldas 2011; ANH-Antek S.A. 2013). Suárez (2007) studied the Colombian Pacific provinces using a data set including seismic, gravimetric, and aeromagnetometric data. Additional geological and tectonic data can be searched in publications by Suárez (2007), Echeverri et al. (2011), and Echeverri et al. (2015). Stratigraphic studies of the area have been published by Cediel et al. (2010) based on the description of the Chagüi-1, Majagua-1 y Remolino Grande-1 stratigraphic wells.

In brief, the basement of the Tumaco basin is interpreted as an allochthonous block composed of fragments of oceanic plateau (Kerr et al. 2002) and the Santonian–Campanian arc of islands, accreted to the continent during the late Cretaceous and early Paleocene (ANH-Universidad de Caldas 2011). The following discussion about geological setting and regional stratigraphy is taken from the technical report presented by Antek S.A. to the National Hydrocarbon Agency (NHA), Colombia (ANH-Antek S.A. 2013).

The Tumaco formation (Chatiense-early Tortoniense) is composed of interbedded mudstones, arenite, and occasionally conglomerates covering the bottom of Tumaco 1-ST-P well (interval 11,980–5381 ft), which has a thickness greater than the 6599 ft (the base is not present). The rocks of this unit can be grouped into eight facies associations represented by bar and estuarine channels, mouth bar, coastal lagoon, proximal front deltaic, prodelta, and platform deposits, respectively.

In the facies associated with the Tumaco Fm, occur occasional mudstones, sandstones and conglomerates, abundant fossils of marine affinity and evidence of rocks associated with deltaic paleoenvironment with the influence from the continent, it allows considering the existence during the late Oligocene and much of the Miocene of an enormous deltaic complex dominated by waves and tides. It seems to correspond to the paleodelta of the Patia River when it disembogued in the area now occupied by the Tumaco Bay.

The Tumaco Fm origin indicates an input area that, at least partially, involved sectors of the Central Cordillera that were recorded in the stratigraphic record with the presence of minerals such as garnets and pumpellyite and fragments of metamorphic rocks such as marbles, although there is a clear preponderance of a mafic–intermediate source area and some recycled rocks of the first cycle.

The Tangareal del Mira Fm (middle Tortoniense-Zancliense), rests unconformably on the Tumaco Fm covering the interval between 1437 and 5381 ft (thickness 3944 ft). In general, the unit consists of interbedded lithic sandstones and mudstones with a development of conglomerates at the base that can be grouped into five associations of facies representing river channels, bar and fluvial channels, bay estuarine, prodelta, and front deltaic deposits.

As in Tumaco Fm, the set of facies and facies associations of Tangareal del Mira Fm allow us to observe the presence of abundant fossils of marine affinity and evidence of continental contribution that would support the existence of a deltaic complex dominated by waves and tides occurs with migration north Mira River in the late Miocene, the position left to the Patia River Delta in its movement to its present site mouth. The development of fluvial facies at the base of the unit, showing the relative fall of sea level in the area, which is succeeded by two transgressive–regressive greater cycles, where is evident a high volcanic influence.

The Cascajal formation (Zancliense), which was examined in detailed in Tumaco-1-ST-S well, since in Tumaco-1-ST-P well, only cuttings were available and partially in some outcrops located on the Tumaco Bay; it is composed of interbedded mudstones, litoarenites, and conglomerate facies, locally bioturbated, it reposes unconformably on the Tangareal del Mira Fm. Moreover, it may be characterized in five associations of facies represented by the proximal deltaic front, distal deltaic front, channels, and estuarine bars, mouth bar, and prodelta deposits (ANH-Universidad de Caldas 2011; ANH-Antek S.A. 2013).

The facies associated with Cascajal formation allow to observe the presence of bioturbated segments, abundant fossils of marine affinity and the continental influence that would support the existence during the late Pliocene of a deltaic complex dominated by waves and tides (Fig. 4) which is associated with the progradation of the delta of Mira River. In this unit, the volcanic contribution is even greater than in the Tangareal del Mira.

The Quaternary is represented by the first 110.89 ft of Tumaco 1-ST-S well (ANH-Universidad de Caldas 2011), which corresponds to fluvial deposits of the Mira River. These deposits consist of interbedded litoarenites and sublitoarenites, massive mudstones, and occasional interbedded polymictic conglomerates with a significant contribution of volcanic rocks.

Samples and experimental

Samples

Samples were selected from the stratigraphic column in the interval 750 to 12,000 ft covering the Miocene to the late Oligocene in the Tumaco-1-ST-P well. Two hundred and fifty samples were analyzed for TOC and RE-Py, 25 samples for vitrinite reflectance, and 100 samples for extractable organic matter (EOM), SARA fractionation, GC/FID, and GCMS analyses applying Antek S.A. geochemical validated procedures, which are part of its ONAC-ISO-17025 quality assurance manual (Antek S.A. 2011). All the samples were picked and washed to remove any contaminant. After the samples had been air-dried or oven-dried, they were crushed on porcelain mortar and pestle up to 62 µm for screening analysis, organic matter extraction, and biomarkers analysis.

Total organic carbon (TOC) and Rock–Eval pyrolysis (RE-Py)

For TOC analysis, 1 g of rock and cutting powder were digested overnight with 10% HCl to remove the carbonate, then washed and dried in oven at 60 °C for 24 h. Approximately 100 mg of sample was transferred onto a Leco cell and mixed with copper/iron catalyst. TOC analysis was run on a Leco S-200 carbon analyzer. Rock–Eval pyrolysis analysis was done in a Vinci-VI instrument with temperature programmed from 30 to 600 °C at 30 °C/min rate. Helium was maintained at 60 mL/min. S1, S2 peaks and Tmax were detected by FID detector, while S3 peak was quantitated by TCD detector.

Organic petrography (vitrinite reflectance)

All samples presented a relatively poor dispersed organic matter that it was necessary to make a organic matter concentration with zinc chloride (ZnCl2), a heavy liquid prepared at a density of near 2 g/mL (ICCP 1963; ISO 1985, 1994; Pawlewicz 2013). Vitrinite reflectance analysis was conducted according to ASTM D-7708-11 and ISO-7404 standard methods. The measurements were done using a Carl Zeiss model Axio-Imager-100 petrographic microscope equipped with reflected and fluorescence UV light in the spectral range between 200 and 3000 nm. The microscope was coupling to a Craic model CoalPro spectrophotometer and a high-speed high-resolution photographic camera. The system was calibrated using a 0.4, 0.9, 1.7, and 5.3% synthetic standards. The microphotometer was equipped with an oil immersion objective (X50/0.85). The oil immersion used has a refraction index of 1.5189 at 23 °C over sodium light at 589.3 nm. The reflectance was measured with normal incident monochromatic light at wavelength of 546 nm.

Organic matter extraction and fractionation (EOM and SARA analyses)

Rock powder samples were extracted using a Dionex ASE-200 accelerated extraction equipment. The solvent was 100% DCM. The extraction condition were solvent pressure at 1500 psi, extraction cell temperature of 100 °C, static pressure time of 2 min, solvent flush 75%, and nitrogen purge time of 60 s. After extraction, the solvent was removed until almost dried by rotaevaporation in a Buchi model 130 rotaevaporator and then transferred in a 4 mL pre-weighted vial. Finally, the extracts were dried with a nitrogen stream and the extractable organic matter (EOM) was determined by gravimetry.

Due to the low EOM content, all the bituminous extracts were used for SARA fractionation by microcolumnation on alumina. The bituminous extracts were dissolved in an excess of n-pentane, and the asphaltenes were precipitated overnight at -10 °C into the refrigerator. Asphaltenes were separated from maltene fraction by centrifugation. The maltene was fractionated by liquid chromatography on activated silica gel in saturates, aromatics, and resins. The saturated fraction was eluted with n-hexane; the aromatic fraction was eluted with n-hexane: dichloromethane (70:30), and the polar (NSO) fraction was eluted with dichloromethane: methanol (98:2). The saturated fraction was analyzed by GC/FID. The branched and cyclic fractions (biomarkers) were separated from n-alkanes by silicalite powder S-115 and then analyzed by SIM-GC/MS. The aromatic fractions were analyzed directly by GC/FID, and some selected samples were analyzed for aromatic biomarkers by gas chromatography-mass spectrometry (SIM-GC/MS).

C15 + saturated fraction by GC/FID

C15+ saturated fractions obtained from SARA analysis were dissolved according to the mass with n-hexane (approximately 10 mg/mL) and analyzed using an Agilent 6890 HRGC/FID fitting with a DB-1 60 m × 0.25 mm × 0.25 μm capillary column. Samples were injected in splitless mode. The GC oven temperature was programmed from 60 to 320 °C at 5 °C/min. Helium was used as carrier gas at a linear velocity of 50 cm/s (12 psig). Injector/detector was maintained at 320 °C/350 °C, respectively. Data handling was done with Agilent Chemstation version 10 chromatographic software.

Biomarkers by GC/MS-SIM

SIM-GC/MS of branched and cyclic and aromatic hydrocarbons was analyzed using an Agilent 7890B gas chromatograph coupling to an Agilent 5975C VL MSD mass spectrometer. The separation was carried out using a Restek Rtx-5MS of 60 m × 0.25 mm × 0.25 µm capillary column operated at constant flow (1 mL/min) (initial head column pressure of 8.23 psi) and the linear velocity of 20 cm/s. Column program started at 60 °C (2 min) to 320 °C at 3 °C/min and maintained at 320 °C for 11 °C/min. The ion source was operated in electronic impact (EI) mode at 70 eV at 150 °C. The MS was operated in selective ion monitoring (SIM) for the following saturate ions: internal standard, Squalane (m/z 99 and 113); n-alkanes (m/z 99); isoprenoids (m/z 183), terpanes (m/z 191), demethylated hopanes (m/z 177), steranes (m/z 217 and 218) and aromatic ions: alkylnaphthalenes (m/z 128, 142, 156, 170), alkylphenanthrenes (m/z 178), alkyldibenzothiophenes (m/z 184), monoaromatic steroids (m/z 253), and triaromatic steroids (m/z 253). The Agilent ChemStation version A02.00 (2012) was utilized as data acquisition system. Biomarker quantitation was done using the area peaks from the GC/MS traces.

Results and discussions

Total organic carbon (TOC) and Rock–Eval pyrolysis

TOC and Rock–Eval pyrolysis results are summarized in Table 1. TOC content analyzed by Leco carbon analyzer, after removal of carbonate minerals, showed values ranging between 0.09 and 2.30 wt%. The major TOC values were found in the deepest intervals of the Tumaco-1-ST-P well (11,610–11,700 ft), which were deposited on calcareous and siliceous siltstones corresponding to the late Oligocene sequence. 47% of the samples analyzed are grouped in the range between 0.5 and 1.0 wt%, which are considered with fair source rock potential. 38% of the samples are classified as O.M. with good quality. Finally, 13% of the total of 250 rock samples analyzed showed TOC values < 0.5%. Rocks organically poor with TOC < 0.5% are considered, in almost all the cases, like rocks with poor generator potential (Bordenave 1993; Peters and Cassa 1994; Hall et al. 2016) therefore, without economic interest.
Table 1

Present-day and original TOC and Rock–Eval pyrolysis parameters for Tumaco-1-ST-P well, Tumaco basin, Colombia

Sample I.D.

Depth (Ft)

Estrat. unit

Lithology

TOC (%)

TOCo (wt%)

S1 (mgHC/g)

S2 (mgHC/g)

S3 (mgCO2/g)

Tmax (°C)

H.I. S2 × 100/TOC

HIo (mg/gTOC)

O.I. (S3 × 100/TOC)

S1/TOC (%)

P.I.

S1/S1 + S2

T.R. (%)

Ro (%)

Rc (%)

T-750

750

Cascajal Fm

Sandstone

0.93

0.95

0.04

0.40

1.54

341

43

47

166

4.30

0.09

9

T-770

770

Cascajal Fm

Sandstone

0.50

0.51

0.05

0.76

1.3

336

152

171

260

10.0

0.06

6

T-790

790

Cascajal Fm

Sandstone

0.22

0.23

0.03

0.11

0.44

344

50

63

200

13.6

0.21

21

T-850

850

Cascajal Fm

Calcareous sandstone

0.09

0.09

0.05

0.17

0.63

338

189

234

700

55.6

0.23

23

T-970

970

Cascajal Fm

Sandstone

0.53

0.54

0.03

0.07

1.19

405

13

19

225

5.70

0.30

30

0.313

T-990

990

Cascajal Fm

Sandstone

0.32

0.33

0.03

0.07

0.97

424

22

31

303

9.40

0.30

30

0.472

T-1050

1050

Cascajal Fm

Siltstone

0.74

0.76

0.06

0.34

1.37

417

46

54

185

8.10

0.15

15

0.346

T-1130

1130

Cascajal Fm

Siltstone

1.91

1.96

0.08

1.85

2.49

341

97

101

130

4.20

0.04

4

T-1190

1190

Cascajal Fm

Sandstone

1.29

1.33

0.14

1.79

3.65

336

139

149

283

10.9

0.07

7

T-1270

1270

Cascajal Fm

Mudstone

0.48

0.6

0.4

4.93

5.33

335

1027

1039

1110

83.3

0.08

8

0.4456

T-1290

1290

Cascajal Fm

Siltstone

1.14

1.17

0.04

0.31

1.17

399

27

30

103

3.50

0.11

11

T-1470

1470

Tangareal de Mira Fm

Siltstone

0.73

0.93

0.06

7.48

7.6

328

1025

1038

1041

100.0

0.09

9

T-1950

1950

Tangareal de Mira Fm

Siltstone

0.51

0.53

0.08

0.6

1.39

364

118

133

273

15.7

0.12

12

T-2150

2150

Tangareal de Mira Fm

Siltstone

0.27

0.28

0.06

0.46

0.88

365

170

190

326

22.2

0.12

12

T-2170

2170

Tangareal de Mira Fm

Siltstone

0.23

0.24

0.04

0.41

1.22

333

178

193

530

17.4

0.09

9

0.3655

T-2370

2370

Tangareal de Mira Fm

Calcareous sandstone

0.7

0.72

0.08

1.20

3.22

412

171

180

460

11.4

0.06

6

0.256

T-2490

2490

Tangareal de Mira Fm

Sandstone

0.92

0.94

0.06

0.44

1.65

413

48

55

179

6.5

0.12

12

0.274

T-2550

2550

Tangareal de Mira Fm

Calcareous siltstone

1.46

1.5

0.06

1

2.78

335

68

71

190

4.1

0.06

6

0.3915

T-2570

2570

Tangareal de Mira Fm

Sandstone

1.32

1.36

0.08

0.81

2.38

365

61

67

180

6.1

0.09

9

T-2590

2590

Tangareal de Mira Fm

Sandstone

1.17

1.2

0.11

0.93

3.56

385

79

89

304

9.4

0.11

11

T-2610

2610

Tangareal de Mira Fm

Calcareous sandstone

1.11

1.14

0.08

0.63

1.94

384

57

64

175

7.2

0.11

11

T-2650

2650

Tangareal de Mira Fm

Calcareous sandstone

0.97

1.00

0.06

0.93

2.41

335

96

102

248

6.2

0.06

6

T-2690

2690

Tangareal de Mira Fm

Calcareous sandstone

0.88

0.90

0.07

0.43

1.64

398

49

57

186

8.0

0.14

14

T-2710

2710

Tangareal de Mira Fm

Calcareous sandstone

0.74

0.76

0.06

0.43

2.01

415

58

66

272

8.1

0.12

12

0.310

T-3010

3010

Tangareal de Mira Fm

Calcareous siltstone

0.66

0.68

0.05

0.52

1.89

426

79

87

286

7.6

0.09

9

0.4305

0.508

T-3030

3030

Tangareal de Mira Fm

Sandstone

0.72

0.74

0.05

0.58

2.25

418

81

88

313

6.9

0.08

8

0.364

T-3490

3490

Tangareal de Mira Fm

Sandstone

0.49

0.50

0.04

0.36

1.31

431

73

81

267

8.2

0.10

10

0.598

T-3770

3770

Tangareal de Mira Fm

Sandstone

0.57

0.59

0.06

0.67

1.46

331

118

128

256

10.5

0.08

8

T-4090

4090

Tangareal de Mira Fm

Calcareous siltstone

0.92

0.95

0.05

1.00

0.8

426

109

115

87

5.4

0.05

5

0.508

T-4130

4130

Tangareal de Mira Fm

Sandstone

0.98

1.01

0.06

1.11

1.28

424

113

119

131

6.1

0.05

5

0.472

T-4330

4330

Tangareal de Mira Fm

Calcareous siltstone

1.63

1.68

0.1

3.47

1.67

428

213

218

102

6.1

0.03

3

0.544

T-4410

4410

Tangareal de Mira Fm

Calcareous sandstone

1.39

1.43

0.09

2.61

1.28

424

188

193

92

6.5

0.03

3

0.472

T-4470

4470

Tangareal de Mira Fm

Calcareous sandstone

1.81

1.86

0.12

3.23

1.42

426

178

185

78

6.6

0.04

4

0.508

T-4550

4550

Tangareal de Mira Fm

Calcareous siltstone

0.77

0.79

0.07

0.87

0.95

424

113

121

123

9.1

0.07

7

0.472

T-4730

4730

Tangareal de Mira Fm

Sandstone

0.48

0.49

0.06

0.45

0.97

417

94

107

202

12.5

0.12

12

0.3718

0.346

T-4750

4750

Tangareal de Mira Fm

Calcareous sandstone

0.36

0.37

0.08

0.58

1.04

360

161

180

289

22.2

0.12

12

T-4810

4810

Tangareal de Mira Fm

Calcareous sandstone

0.40

0.41

0.11

1.13

0.92

350

283

304

230

27.5

0.09

9

T-4830

4830

Tangareal de Mira Fm

Calcareous siltstone

0.38

0.39

0.09

1.01

0.83

353

266

284

218

23.7

0.08

8

T-5030

5030

Tangareal de Mira Fm

Calcareous sandstone

1.25

1.29

0.18

4.18

2.82

432

334

344

226

14.4

0.04

4

0.616

T-5394

5394

Tangareal de Mira Fm

Calcareous mudstone

1.26

1.30

0.09

2.73

1.15

431

217

224

91

7.1

0.03

3

0.598

T-5458

5458

Tangareal de Mira Fm

Mudstone

0.44

0.45

0.05

0.44

0.66

415

100

110

150

11.4

0.10

10

0.310

T-5475

5475

Tumaco Fm

Mudstone

1.85

1.90

0.07

1.21

1.46

431

65

68

79

3.8

0.05

5

0.598

T-5509

5509

Tumaco Fm

Calcareous mudstone

1.25

1.29

0.09

2.51

1.9

431

201

207

152

7.2

0.03

3

0.1978

0.598

T-5526

5526

Tumaco Fm

Calcareous mudstone

0.9

0.93

0.07

1.07

0.97

426

119

126

108

7.8

0.06

6

0.508

T-5536

5536

Tumaco Fm

Mudstone

0.94

0.97

0.09

1.46

1.22

429

155

165

130

9.6

0.06

6

0.562

T-5543

5543

Tumaco Fm

Calcareous mudstone

1.11

1.14

0.1

2.14

1.58

432

193

201

142

9.0

0.04

4

0.616

T-5560

5560

Tumaco Fm

Calcareous siltstone

1.67

1.72

0.1

3.72

1.82

431

223

229

109

6.0

0.03

3

0.598

T-5570

5570

Tumaco Fm

Calcareous sandstone

1.99

2.05

0.47

10.45

1.1

416

525

537

55

23.6

0.04

4

0.3706

0.328

T-5650

5650

Tumaco Fm

Calcareous siltstone

1.29

1.33

0.08

1.43

1.33

425

111

117

103

6.2

0.05

5

0.49

T-5730

5730

Tumaco Fm

Sandstone

0.96

0.99

0.08

3.25

0.88

421

339

344

92

8.3

0.02

2

0.418

T-5750

5750

Tumaco Fm

Calcareous siltstone

1.53

1.58

0.09

2.39

1.21

418

156

162

79

5.9

0.04

4

0.364

T-5810

5810

Tumaco Fm

Siltstone

1.15

1.19

0.09

3.33

0.86

423

290

297

75

7.8

0.03

3

0.454

T-5890

5890

Tumaco Fm

Calcareous siltstone

1.14

1.17

0.08

1.92

1.11

428

168

174

97

7.0

0.04

4

0.4227

0.544

T-5910

5910

Tumaco Fm

Siltstone

1.13

1.16

0.07

1.59

0.91

429

141

147

81

6.2

0.04

4

0.562

T-5950

5950

Tumaco Fm

Calcareous siltstone

1.15

1.18

0.04

1.46

0.82

429

127

131

71

3.5

0.03

3

0.562

T-5990

5990

Tumaco Fm

Calcareous siltstone

1.46

1.50

0.04

1.65

0.81

430

113

115

55

2.7

0.02

2

0.580

T-6010

6010

Tumaco Fm

Siltstone

1.19

1.22

0.06

1.46

1.2

422

123

128

101

5.0

0.04

4

0.436

T-6070

6070

Tumaco Fm

Calcareous sandstone

1.39

1.43

0.05

2.51

1.02

425

181

185

73

3.6

0.02

2

0.355

0.490

T-6090

6090

Tumaco Fm

Calcareous siltstone

1.44

1.48

0.05

2.12

1.06

431

147

150

74

3.5

0.02

2

0.598

T-6110

6110

Tumaco Fm

Calcareous sandstone

1.12

1.15

0.05

1.23

1.23

418

110

115

110

4.5

0.04

4

0.364

T-6130

6130

Tumaco Fm

Calcareous sandstone

1.56

1.60

0.07

0.84

1.5

420

54

59

96

4.5

0.08

8

0.400

T-6150

6150

Tumaco Fm

Siltstone

1.63

1.67

0.06

2.66

1.21

426

163

166

74

3.7

0.02

2

0.508

T-6170

6170

Tumaco Fm

Calcareous sandstone

1.73

1.78

0.06

2.28

0.91

429

132

136

53

3.5

0.03

3

0.4792

0.562

T-6190

6190

Tumaco Fm

Siltstone

1.58

1.63

0.08

2.42

1.09

431

153

158

69

5.1

0.03

3

0.598

T-6210

6210

Tumaco Fm

Calcareous siltstone

1.21

1.25

0.1

2.67

1.33

427

221

229

110

8.3

0.04

4

0.526

T-6250

6250

Tumaco Fm

Calcareous siltstone

1.48

1.52

0.09

2.14

1.11

429

145

151

75

6.1

0.04

4

0.562

T-6310

6310

Tumaco Fm

Calcareous sandstone

1.11

1.14

0.07

0.92

1.26

422

83

89

114

6.3

0.07

7

0.436

T-6330

6330

Tumaco Fm

Calcareous siltstone

1.36

1.40

0.07

1.35

0.85

427

99

104

63

5.1

0.05

5

0.4196

0.526

T-6390

6390

Tumaco Fm

Calcareous sandstone

1.22

1.25

0.05

1.17

1.16

422

96

100

95

4.1

0.04

4

0.436

T-6430

6430

Tumaco Fm

Sandstone

1.04

1.07

0.06

1.73

0.67

419

166

171

64

5.8

0.03

3

0.382

T-6550

6550

Tumaco Fm

Sandstone

1.33

1.37

0.09

1.83

1.14

428

138

145

86

6.8

0.05

5

0.544

T-6570

6570

Tumaco Fm

Sandstone

1.17

1.2

0.06

1.64

1.07

429

140

146

91

5.1

0.04

4

0.562

T-6590

6590

Tumaco Fm

Siltstone

1.35

1.39

0.06

1.16

1.33

422

86

91

99

4.4

0.05

5

0.436

T-6630

6630

Tumaco Fm

Siltstone

1.35

1.39

0.09

1.45

1.22

423

107

114

90

6.7

0.06

6

0.454

T-6710

6710

Tumaco Fm

Calcareous siltstone

1.25

1.28

0.05

1.48

0.99

426

118

122

79

4.0

0.03

3

0.508

T-6750

6750

Tumaco Fm

Sandstone

1.18

1.21

0.11

1.76

0.89

429

149

158

75

9.3

0.06

6

0.562

T-6770

6770

Tumaco Fm

Calcareous siltstone

1.14

1.17

0.05

1.74

0.85

428

153

157

75

4.4

0.03

3

0.544

T-6790

6790

Tumaco Fm

Calcareous sandstone

1.36

1.40

0.06

1.90

0.95

428

140

144

70

4.4

0.03

3

0.4248

0.544

T-6810

6810

Tumaco Fm

Calcareous sandstone

1.13

1.16

0.06

1.64

0.78

429

145

151

69

5.3

0.04

4

0.562

T-6830

6830

Tumaco Fm

Calcareous sandstone

1.2

1.23

0.05

1.58

0.9

429

132

136

75

4.2

0.03

3

0.562

T-6850

6850

Tumaco Fm

Calcareous sandstone

1.18

1.21

0.05

1.76

0.69

429

149

153

58

4.2

0.03

3

0.562

T-6890

6890

Tumaco Fm

Siltstone

1.17

1.2

0.07

1.62

0.89

424

138

143

76

6.0

0.04

4

0.472

T-6930

6930

Tumaco Fm

Sandstone

0.96

0.99

0.05

1.14

0.77

428

119

123

80

5.2

0.04

4

0.364

0.544

T-6970

6970

Tumaco Fm

Siltstone

0.8

0.82

0.05

0.97

0.56

416

121

126.7

70

6.3

0.05

5

0.328

T-7050

7011

Tumaco Fm

Calcareous mudstone

0.45

0.46

0.09

0.43

0.93

365

96

114

207

20.0

0.17

17

T-7110

7043

Tumaco Fm

Calcareous mudstone

0.76

0.78

0.03

0.25

0.98

417

33

37

129

3.9

0.10

11

0.346

T-7011

7050

Tumaco Fm

Calcareous mudstone

1.76

1.82

0.29

6.79

0.99

418

386

397

56

16.5

0.04

4

0.364

T-7043

7110

Tumaco Fm

Siltstone

1.18

1.22

0.1

2.51

0.83

422

213

220

70

8.5

0.04

4

0.3946

0.436

T-7130

7130

Tumaco Fm

Calcareous sandstone

1.08

1.11

0.08

2.49

0.6

420

231

237

56

7.4

0.03

3

0.400

T-7210

7210

Tumaco Fm

Calcareous sandstone

1.16

1.19

0.12

1.70

0.88

419

147

157

76

10.3

0.07

7

0.4081

0.382

T-7230

7230

Tumaco Fm

Calcareous siltstone

1.09

1.12

0.07

1.82

0.7

422

167

173

64

6.4

0.04

4

0.436

T-7290

7290

Tumaco Fm

Calcareous siltstone

1.07

1.1

0.06

1.21

0.77

420

118

119

72

5.6

0.05

5

0.400

T-7310

7310

Tumaco Fm

Calcareous Siltstone

1.06

1.09

0.08

0.90

1.02

415

85

92

96

7.5

0.08

8

0.310

T-7330

7330

Tumaco Fm

Calcareous siltstone

1.09

1.12

0.05

0.67

1.19

415

61

65

109

4.6

0.07

7

0.4113

0.310

T-7370

7370

Tumaco Fm

Calcareous siltstone

0.94

0.97

0.04

0.57

1.04

413

61

65

111

4.3

0.07

7

0.274

T-7450

7450

Tumaco Fm

Calcareous siltstone

1.36

1.4

0.13

2.51

0.97

423

193

195

71

9.6

0.05

5

0.454

T-7453

7453

Tumaco Fm

Calcareous siltstone

0.69

0.71

0.02

0.23

0.81

431

33

36

117

2.9

0.08

8

0.598

T-7470

7470

Tumaco Fm

Siltstone

1.34

1.38

0.12

2.53

0.93

426

189

197

69

9.0

0.05

5

0.508

T-7471

7471

Tumaco Fm

Siltstone

0.91

0.93

0.03

0.33

1.08

426

36

39

119

3.3

0.08

8

0.508

T-7476

7476

Tumaco Fm

Siltstone

0.67

0.69

0.03

0.21

0.87

431

31

36

130

4.5

0.13

13

0.598

T-7488

7488

Tumaco Fm

Siltstone

0.88

0.9

0.03

0.36

1.05

432

41

44

119

3.4

0.08

8

0.3478

0.616

T-7504

7504

Tumaco Fm

Siltstone

0.92

0.94

0.03

0.29

0.84

433

32

35

91

3.3

0.09

9

0.634

T-7522

7522

Tumaco Fm

Siltstone

0.82

0.84

0.03

0.32

0.93

428

39

43

113

3.7

0.09

9

0.544

T-7539.5

7540

Tumaco Fm

Siltstone

0.39

0.4

0.04

0.17

0.69

423

44

54

177

10.3

0.19

19

0.454

T-7557

7557

Tumaco Fm

Siltstone

0.52

0.53

0.04

0.18

0.72

427

35

42

138

7.7

0.18

18

0.526

T-7574

7574

Tumaco Fm

Siltstone

0.82

0.84

0.04

0.31

0.88

425

38

43

107

4.9

0.11

11

0.431

0.49

T-7591

7591

Tumaco Fm

Siltstone

1.25

1.28

0.03

0.37

1.22

429

30

33

98

2.4

0.08

8

0.562

T-7609

7609

Tumaco Fm

Siltstone

0.11

0.11

0.04

0.07

0.22

429

64

97

200

36.4

0.36

36

0.562

T-7627

7627

Tumaco Fm

Siltstone

0.82

0.84

0.05

0.29

0.87

429

35

41

106

6.1

0.15

15

0.562

T-7642.5

7643

Tumaco Fm

Sandstone

0.36

0.37

0.04

0.25

0.83

429

69

79

231

1.1

0.14

14

0.562

T-7659

7659

Tumaco Fm

Sandstone

0.59

0.61

0.04

0.23

0.65

432

39

46

110

6.8

0.15

15

0.451

0.616

T-7693

7693

Tumaco Fm

Calcareous mudstone

1.25

1.28

0.04

0.49

1.37

440

39

42

110

3.2

0.08

8

0.760

T-7712

7712

Tumaco Fm

Calcareous mudstone

1.08

1.11

0.03

0.38

1.1

435

35

38

102

2.8

0.07

7

0.670

T-7723

7723

Tumaco Fm

Calcareous mudstone

0.83

0.85

0.04

0.13

0.8

417

16

21

96

4.8

0.24

24

0.4754

0.346

T-7740

7740

Tumaco Fm

Calcareous mudstone

0.51

0.52

0.05

0.23

0.73

425

45

54

143

9.8

0.18

18

0.490

T-7761

7761

Tumaco Fm

Calcareous mudstone

0.85

0.87

0.03

0.30

0.96

429

35

38

113

3.5

0.09

9

0.3782

0.562

T-7777

7777

Tumaco Fm

Calcareous mudstone

1.05

1.08

0.03

0.45

1.06

432

43

46

101

2.9

0.06

6

0.616

T-7795

7795

Tumaco Fm

Mudstone

0.92

0.94

0.04

0.28

0.96

429

30

34

104

4.3

0.13

13

0.562

T-7828

7828

Tumaco Fm

Siltstone

0.85

0.87

0.05

0.31

0.94

429

36

42

111

5.9

0.14

14

0.562

T-7844

7844

Tumaco Fm

Siltstone

0.74

0.76

0.04

0.3

1.00

431

41

46

135

5.4

0.12

12

0.598

T-7856

7856

Tumaco Fm

Calcareous siltstone

0.79

0.81

0.03

0.21

0.82

429

27

31

104

3.8

0.13

13

0.3787

0.562

T-7861

7861

Tumaco Fm

Calcareous siltstone

1.11

1.14

0.03

0.37

0.96

431

33

36

86

2.7

0.08

8

0.598

T-7878

7878

Tumaco Fm

Calcareous siltstone

0.96

0.99

0.04

0.28

1.01

426

29

32

105

4.2

0.13

13

0.508

T-7895

7895

Tumaco Fm

Calcareous siltstone

1.53

1.57

0.04

0.43

1.57

433

28

31

103

2.6

0.09

9

0.634

T-7911

7911

Tumaco Fm

Calcareous siltstone

1.98

2

0.04

0.50

2.11

431

25

27

107

2.0

0.07

7

0.598

T-7928

7928

Tumaco Fm

Sandstone

2.1

2.16

0.04

0.82

1.72

435

39

41

82

1.9

0.05

5

0.3496

0.670

T-7955

7955

Tumaco Fm

Calcareous mudstone

0.88

0.9

0.03

0.38

0.57

433

43

46

65

3.4

0.07

7

0.634

T-7971

7971

Tumaco Fm

Siltstone

2.19

2.25

0.04

0.78

1.87

435

36

38

85

1.8

0.05

5

0.670

T-8017.5

8017.5

Tumaco Fm

Sandstone

0.93

0.95

0.03

0.32

0.95

432

34

37

102

3.2

0.09

9

0.616

T-8045

8045

Tumaco Fm

Siltstone

0.63

0.65

0.03

0.26

0.50

441

41

45

79

4.8

0.10

10

0.778

T-8067

8067

Tumaco Fm

Sandstone

0.92

0.94

0.03

0.4

0.74

432

43

46

80

3.3

0.07

7

0.421

0.616

T-8084

8084

Tumaco Fm

Siltstone

1.04

1.07

0.02

0.37

0.82

433

36

38

79

1.9

0.05

5

0.634

T-8107.5

8107.5

Tumaco Fm

Siltstone

0.13

0.13

0.03

0.09

0.2

440

69

90

154

23.1

0.25

25

0.760

T-8123.5

8123.5

Tumaco Fm

Sandstone

0.22

0.23

0.02

0.11

0.33

426

50

58

150

9.1

0.15

15

0.508

T-8145

8145

Tumaco Fm

Siltstone

1.12

1.15

0.03

0.39

0.79

436

35

38

71

2.7

0.07

7

0.688

T-8160.5

8160.5

Tumaco Fm

Siltstone

0.28

0.29

0.03

0.17

0.38

431

61

71

136

10.7

0.15

15

0.4083

0.598

T-8194

8194

Tumaco Fm

Siltstone

1.02

1.05

0.03

0.34

1.00

431

33

36

98

2.9

0.08

8

0.598

T-8211

8211

Tumaco Fm

Mudstone

1.3

1.33

0.03

0.47

0.95

432

36

38

73

2.3

0.06

6

0.616

T-8233

8233

Tumaco Fm

Calcareous mudstone

1.46

1.5

0.03

0.36

1.65

427

25

27

113

2.1

0.08

8

0.526

T-8243

8243

Tumaco Fm

Calcareous mudstone

1.19

1.12

0.03

0.4

1.37

433

34

36

115

2.5

0.07

7

0.634

T-8255.5

8255.5

Tumaco Fm

Calcareous mudstone

1.89

1.94

0.03

0.54

1.75

433

29

30

93

1.6

0.05

5

0.378

0.634

T-8266

8266

Tumaco Fm

Calcareous siltstone

0.94

0.96

0.03

0.45

1.13

439

48

51

120

3.2

0.06

6

0.742

T-8275

8275

Tumaco Fm

Calcareous siltstone

2.05

2.1

0.04

0.54

2.10

433

26

28

102

2.0

0.07

7

0.634

T-8302.5

8302.5

Tumaco Fm

Siltstone

1.36

1.4

0.05

0.82

1.24

435

60

64

91

3.7

0.06

6

0.67

T-8312.5

8312.5

Tumaco Fm

Siltstone

1.16

1.19

0.04

0.58

1.16

438

50

53

100

3.4

0.06

6

0.3977

0.724

T-8317

8317

Tumaco Fm

Calcareous siltstone

1.19

1.22

0.04

0.59

0.99

434

50

53

83

3.4

0.06

6

0.652

T-8332.5

8332.5

Tumaco Fm

Siltstone

1.53

1.57

0.04

0.71

1.43

437

46

48

93

2.6

0.05

5

0.706

T-8338

8338

Tumaco Fm

Mudstone

1.2

1.23

0.05

0.43

1.36

433

36

40

113

4.2

0.10

10

0.634

T-8354.5

8354.5

Tumaco Fm

Calcareous siltstone

1.31

1.34

0.03

0.43

1.12

434

33

35

85

2.3

0.07

7

0.652

T-8370.5

8370.5

Tumaco Fm

Siltstone

1.3

1.33

0.04

0.36

1.21

432

28

31

93

3.1

0.10

10

0.3599

0.616

T-8380

8380

Tumaco Fm

Siltstone

1.2

1.23

0.05

0.38

1.02

433

32

36

85

4.2

0.12

12

0.634

T-8388

8388

Tumaco Fm

Sandstone

0.65

0.67

0.03

0.25

0.71

433

38

43

109

4.6

0.11

11

0.634

T-8395

8395

Tumaco Fm

Siltstone

0.55

0.56

0.03

0.15

0.74

431

27

32

135

5.5

0.17

17

0.598

T-8406.8

8406.8

Tumaco Fm

Sandstone

0.96

0.99

0.04

0.33

0.91

432

34

38

95

4.2

0.11

11

0.616

T-8431

8431

Tumaco Fm

Siltstone

1.2

1.23

0.04

0.51

1.16

433

43

46

97

3.3

0.07

7

0.5418

0.634

T-8440

8440

Tumaco Fm

Calcareous siltstone

0.1

0.1

0.04

0.09

0.34

445

90

126

340

40.0

0.31

31

0.4335

0.85

T-8448

8448

Tumaco Fm

Siltstone

0.97

1

0.04

0.34

0.80

436

35

39

82

4.1

0.11

11

0.688

T-8457.5

8457.5

Tumaco Fm

Siltstone

0.85

0.87

0.03

0.21

0.77

435

25

29

91

3.5

0.13

13

0.670

T-8470

8470

Tumaco Fm

Siltstone

1.00

1.03

0.04

0.54

0.92

431

54

58

92

4.0

0.07

7

0.598

T-8487.5

8487.5

Tumaco Fm

Siltstone

0.77

0.79

0.03

0.24

0.85

429

31

35

110

3.9

0.11

11

0.4213

0.562

T-8510

8510

Tumaco Fm

Calcareous sandstone

0.38

0.39

0.03

0.22

0.39

428

58

65

103

7.9

0.12

12

0.544

T-8530

8530

Tumaco Fm

Calcareous sandstone

0.65

0.67

0.03

0.39

0.68

420

60

64

105

4.6

0.07

7

0.400

T-8550

8550

Tumaco Fm

Calcareous sandstone

0.36

0.37

0.05

0.31

0.80

415

86

99

222

13.9

0.14

14

0.310

T-8590

8590

Tumaco Fm

Calcareous sandstone

0.50

0.51

0.06

0.48

0.71

415

96

107

142

12.0

0.11

11

0.310

T-8650

8650

Tumaco Fm

Calcareous sandstone

0.42

0.43

0.04

0.32

0.63

415

76

85

150

9.5

0.11

11

0.310

T-8710

8710

Tumaco Fm

Calcareous sandstone

0.81

0.83

0.1

0.79

0.95

417

98

109

117

1.3

0.11

11

0.346

T-8770

8770

Tumaco Fm

Siltstone

0.78

0.8

0.07

0.58

0.78

425

74

83

100

9.0

0.11

11

0.490

T-8850

8850

Tumaco Fm

Siltstone

1.24

1.27

0.03

0.73

0.99

431

59

61

80

2.4

0.04

4

0.598

T-8870

8870

Tumaco Fm

Calcareous sandstone

2.04

2.09

0.07

1

1.63

432

49

53

80

3.4

0.07

7

0.5201

0.616

T-8890

8890

Tumaco Fm

Calcareous sandstone

1.58

1.62

0.06

0.95

1.41

431

60

64

89

3.8

0.06

6

0.598

T-9050

9050

Tumaco Fm

Calcareous sandstone

0.81

0.83

0.04

0.54

1.04

429

67

72

128

4.9

0.07

7

0.562

T-9070

9070

Tumaco Fm

Siltstone

0.77

0.79

0.05

0.68

0.98

429

88

94

127

6.5

0.07

7

0.562

T-9150

9150

Tumaco Fm

Calcareous siltstone

1.20

1.23

0.05

0.77

1.11

429

64

68

93

4.2

0.06

6

0.562

T-9230

9230

Tumaco Fm

Calcareous siltstone

0.66

0.68

0.08

0.53

0.61

417

80

91

92

12.1

0.13

13

0.346

T-9250

9250

Tumaco Fm

Calcareous sandstone

0.66

0.68

0.06

0.44

0.59

417

67

76

89

9.1

0.12

12

0.346

T-9310

9310

Tumaco Fm

Calcareous siltstone

0.92

0.94

0.05

0.54

0.90

423

59

64

98

5.4

0.08

8

0.562

T-9390

9390

Tumaco Fm

Calcareous sandstone

0.67

0.69

0.09

0.91

0.84

422

136

148

125

13.4

0.09

9

0.562

T-9430

9430

Tumaco Fm

Calcareous siltstone

0.74

0.76

0.14

1.32

1.07

366

178

195

145

18.9

0.10

10

T-9470

9470

Tumaco Fm

Calcareous sandstone

0.68

0.7

0.06

0.68

0.70

424

100

108

103

8.8

0.08

8

0.410

0.472

T-9490

9490

Tumaco Fm

Calcareous siltstone

0.78

0.8

0.07

0.72

0.73

422

92

100

94

9.0

0.09

9

0.436

T-9550

9550

Tumaco Fm

Calcareous siltstone

0.89

0.91

0.06

0.79

0.67

427

89

96

75

6.7

0.07

7

0.526

T-9610

9610

Tumaco Fm

Calcareous siltstone

0.71

0.73

0.07

0.61

0.57

428

86

95

80

9.9

0.10

10

0.544

T-9630

9630

Tumaco Fm

Calcareous siltstone

0.69

0.71

0.03

0.56

0.54

429

81

85

78

4.3

0.05

5

0.562

T-9710

9710

Tumaco Fm

Calcareous sandstone

0.58

0.6

0.05

0.43

0.54

427

74

82

93

8.6

0.10

10

0.4033

0.526

T-9790

9790

Tumaco Fm

Calcareous sandstone

1.15

1.18

0.09

0.81

0.63

425

70

77

55

7.8

0.10

10

0.490

T-9810

9810

Tumaco Fm

Sandstone

0.57

0.59

0.08

0.64

0.59

426

112

124

104

14.0

0.11

11

0.508

T-9870

9870

Tumaco Fm

Calcareous siltstone

0.65

0.67

0.07

0.66

0.68

422

102

112

105

10.8

0.10

10

0.436

T-9950

9950

Tumaco Fm

Calcareous siltstone

0.75

0.77

0.06

0.66

0.62

423

88

95

83

8.0

0.08

8

0.454

T-9990

9990

Tumaco Fm

Calcareous siltstone

0.63

0.65

0.06

0.61

0.64

419

97

106

102

9.5

0.09

9

0.3577

0.382

T-10015

10015

Tumaco Fm

Siltstone

0.48

0.49

0.03

0.27

0.36

434

56

62

75

6.3

0.10

10

0.652

T-10026

10,026

Tumaco Fm

Siltstone

0.55

0.57

0.04

0.46

0.44

415

84

91

80

7.3

0.08

8

0.31

T-10030

10030

Tumaco Fm

Siltstone

0.89

0.92

0.07

1

0.65

429

112

120

73

7.9

0.07

7

0.562

T-10033

10,033

Tumaco Fm

Calcareous siltstone

0.80

0.82

0.05

0.73

0.6

428

91

96

75

6.3

0.06

6

0.544

T-10046

10,046

Tumaco Fm

Siltstone

0.66

0.68

0.05

0.49

0.6

432

74

81

91

7.6

0.09

9

0.616

T-10051

10,051

Tumaco Fm

Siltstone

0.64

0.66

0.05

0.4

0.62

431

63

70

97

7.8

0.11

11

0.5131

0.598

T-10059

10,059

Tumaco Fm

Siltstone

0.81

0.83

0.04

0.44

0.57

429

54

58

70

4.9

0.08

8

0.562

T-10069

10,069

Tumaco Fm

Mudstone

0.84

0.86

0.04

0.79

0.49

431

94

99

58

4.8

0.05

5

0.598

T-10079

10,079

Tumaco Fm

Mudstone

1.00

1.03

0.05

1.01

0.63

433

101

106

63

5.0

0.05

5

0.634

T-10087

10,087

Tumaco Fm

Mudstone

0.57

0.59

0.02

0.25

0.5

429

44

47

88

3.5

0.07

7

0.562

T-10098

10,098

Tumaco Fm

Mudstone

0.80

0.82

0.03

0.47

0.65

432

59

63

81

3.8

0.06

6

0.3691

0.616

T-10105

10,105

Tumaco Fm

Mudstone

0.46

0.47

0.03

0.36

0.48

432

78

84

104

6.5

0.08

8

0.616

T-10125

10,125

Tumaco Fm

Mudstone

0.41

0.42

0.03

0.29

0.53

432

71

78

129

7.3

0.09

9

0.616

T-10135.5

10,135.5

Tumaco Fm

Mudstone

0.61

0.63

0.03

0.38

0.4

433

62

66

66

4.9

0.07

7

0.634

T-10142

10,142

Tumaco Fm

Siltstone

0.85

0.87

0.04

0.56

0.66

433

66

71

78

4.7

0.07

7

0.634

T-10162

10,162

Tumaco Fm

Siltstone

0.60

0.62

0.03

0.34

0.56

430

57

62

93

5.0

0.08

8

0.384

0.58

T-10175

10,175

Tumaco Fm

Calcareous siltstone

0.52

0.53

0.03

0.36

0.45

432

69

75

87

5.8

0.08

8

0.616

T-10184

10,184

Tumaco Fm

Siltstone

0.72

0.74

0.03

0.52

0.47

433

72

76

65

4.2

0.05

5

0.634

T-10196.5

10,196.5

Tumaco Fm

Siltstone

0.82

0.84

0.04

0.57

0.52

431

70

75

63

4.9

0.07

7

0.598

T-10209

10,209

Tumaco Fm

Siltstone

0.64

0.66

0.03

0.39

0.66

431

61

65

103

4.7

0.07

7

0.598

T-10226

10,226

Tumaco Fm

Siltstone

0.77

0.79

0.04

0.52

0.58

430

68

73

75

5.2

0.07

7

0.3616

0.58

T-10241.5

10,241.5

Tumaco Fm

Siltstone

0.70

0.72

0.04

0.54

0.51

433

77

82

73

5.7

0.07

7

0.634

T-10251

10,251

Tumaco Fm

Siltstone

0.69

0.71

0.04

0.52

0.46

432

75

80

67

5.8

0.07

7

0.616

T-10259

10,259

Tumaco Fm

Siltstone

0.67

0.69

0.05

0.54

0.66

431

81

88

99

7.5

0.08

8

0.598

T-10269

10,269

Tumaco Fm

Siltstone

0.54

0.55

0.03

0.37

0.53

431

69

75

98

5.6

0.08

8

0.598

T-10276

10,276

Tumaco Fm

Siltstone

0.61

0.63

0.04

0.38

0.5

431

62

69

82

6.6

0.10

10

0.371

0.598

T-10349

10,349

Tumaco Fm

Siltstone

0.77

0.79

0.03

0.47

0.63

431

61

65

82

3.9

0.06

6

0.4157

0.598

T-10390

10,390

Tumaco Fm

Calcareous sandstone

0.81

0.83

0.08

0.71

1.06

424

88

97

131

9.9

0.10

10

0.472

T-10410

10,410

Tumaco Fm

Calcareous siltstone

0.42

0.43

0.07

0.67

1.16

336

160

174

276

1.7

0.09

9

T-10450

10,450

Tumaco Fm

Calcareous sandstone

0.72

0.74

0.06

0.56

0.88

429

78

86

122

8.3

0.10

10

0.562

T-10470

10,470

Tumaco Fm

Calcareous siltstone

0.45

0.46

0.07

0.62

0.76

429

138

152

169

15.6

0.10

10

0.4523

0.562

T-10610

10,610

Tumaco Fm

Calcareous siltstone

0.58

0.6

0.08

0.46

0.96

368

79

92

166

13.8

0.15

15

T-10630

10,630

Tumaco Fm

Calcareous siltstone

0.36

0.37

0.09

0.54

0.44

424

150

171

122

25.0

0.14

14

0.472

T-10670

10,670

Tumaco Fm

Calcareous sandstone

0.31

0.32

0.09

0.52

0.39

430

168

193

126

29.0

0.15

15

0.580

T-10690

10,690

Tumaco Fm

Calcareous sandstone

0.52

0.53

0.15

0.69

0.73

418

133

158

140

28.8

0.18

18

0.364

T-10770

10,770

Tumaco Fm

Calcareous sandstone

0.66

0.68

0.09

0.64

0.87

423

97

109

132

13.6

0.12

12

0.3929

0.454

T-10850

10,850

Tumaco Fm

Calcareous siltstone

0.73

0.75

0.05

0.67

0.74

426

92

98

101

6.8

0.07

7

0.508

T-10870

10,870

Tumaco Fm

Calcareous siltstone

0.70

0.72

0.08

0.71

0.93

415

101

111

133

11.4

0.10

10

0.310

T-10930

10,930

Tumaco Fm

Calcareous sandstone

0.76

0.78

0.14

1

1.03

366

132

148

136

18.4

0.12

12

T-11010

11,010

Tumaco Fm

Calcareous sandstone

0.66

0.68

0.11

0.79

0.91

367

120

135

138

16.7

0.12

12

T-11030

11,030

Tumaco Fm

Calcareous sandstone

0.55

0.57

0.06

0.61

0.69

417

111

121

125

10.9

0.09

9

0.4268

0.346

T-11050

11,050

Tumaco Fm

Calcareous sandstone

0.68

0.7

0.08

0.65

0.83

374

96

107

122

11.8

0.11

11

T-11090

11,090

Tumaco Fm

Calcareous sandstone

0.45

0.46

0.09

0.74

0.77

353

164

181

171

20.0

0.11

11

T-11170

11,170

Tumaco Fm

Calcareous siltstone

0.64

0.66

0.08

0.58

0.73

381

91

102

114

12.5

0.12

12

T-11230

11,230

Tumaco Fm

Siltstone

0.54

0.55

0.06

0.43

0.64

421

80

90

119

11.1

0.12

12

0.418

T-11250

11,250

Tumaco Fm

Calcareous siltstone

0.43

0.44

0.06

0.39

0.66

364

91

103

153

14.0

0.13

13

T-11330

11,330

Tumaco Fm

Calcareous siltstone

0.61

0.63

0.09

0.82

0.96

358

134

147

157

14.8

0.10

10

T-11410

11,410

Tumaco Fm

Calcareous siltstone

0.69

0.71

0.11

0.9

0.83

365

130

144

120

15.9

0.11

11

T-11430

11,430

Tumaco Fm

Sandstone

0.63

0.65

0.1

0.88

0.71

366

140

154

113

15.9

0.10

10

T-11490

11,490

Tumaco Fm

Sandstone

0.73

0.75

0.09

0.75

0.63

420

103

115

86

12.3

0.11

11

0.400

T-11570

11,570

Tumaco Fm

Calcareous siltstone

1.66

1.71

0.2

1.88

0.84

432

113

124

51

12.0

0.10

10

0.4404

0.616

T-11610

11,610

Tumaco Fm

Calcareous siltstone

2.30

2.36

0.43

4.96

1.16

432

216

231

50

18.7

0.08

8

0.616

T-11650

11,650

Tumaco Fm

Calcareous siltstone

1.76

1.81

0.42

5.83

1.14

432

331

349

65

23.9

0.07

7

0.616

T-11670

11,670

Tumaco Fm

Calcareous sandstone

1.54

1.59

0.25

3.53

1.09

433

229

243

71

16.2

0.07

7

0.634

T-11690

11,690

Tumaco Fm

Calcareous siltstone

2.05

2.11

0.33

4.19

1.17

433

204

217

57

16.1

0.07

7

0.634

T-11710

11,710

Tumaco Fm

Calcareous siltstone

2.13

2.18

0.8

9.49

1.6

431

446

470

75

37.6

0.08

8

0.4700

0.598

T-11730

11,730

Tumaco Fm

Calcareous siltstone

1.27

1.31

0.29

4.56

1.21

431

359

375

95

22.8

0.06

6

0.598

T-11790

11,790

Tumaco Fm

Calcareous siltstone

1.10

1.13

0.16

2.25

0.97

432

205

218

88

14.5

0.07

7

0.616

T-11810

11,810

Tumaco Fm

Calcareous siltstone

1.07

1.1

0.2

2.55

0.72

431

238

252

67

18.7

0.07

7

0.598

T-11870

11,870

Tumaco Fm

Calcareous siltstone

0.99

1.02

0.13

1.66

0.68

435

168

179

69

13.1

0.07

7

0.3938

0.670

T-11930

11,930

Tumaco Fm

Calcareous siltstone

0.81

0.83

0.1

1.03

0.72

431

127

138

89

12.3

0.09

9

0.598

Original TOC and hydrogen index (TOCo and HIo) were calculated using ZetaWare Software, Inc

S1, mgHC/g rock; S2, mgHC/g rock; S3, mgCO2/g rock; rock H.I. = (S2/TOC) × 100; O.I. = (S3/TOC) × 100; P.I., Potential Index; SAT/ARO, saturate/aromatic ratio; –, data not available

Free hydrocarbons (S1 peak) average value was 0.075 mg HC/g rock (ranging between 0.02 and 0.80 mg HC/g rock). The high heterogeneity of S1 through the stratigraphic column is due to the multiple and successive changes of organic facies in the sedimentary strata. Samples collected at 11,570–11,730 ft in the late Oligocene displayed the highest values of S1 ranging between 0.2 and 0.8 mg HC/g rock, while most of the samples had values < 0.25%, which classifies the generation potential as “poor and/or acceptable” (Peters and Cassa 1994). In practical terms, the peak S1 is less than the removable fraction (EOM) for immature sediments; for mature sediments, peak S1 and the content of EOM fraction are fairly comparable (Peter et al. 2005).

S2 values vary between 0.07 and 1 or removal 0.45 mg HC/g rock, with an average of 1.1 ± 1.36 mg HC/g rock. The highest S2 peak values were found in the interval around 11,700 ft in the late Oligocene of the Tumaco Fm. S2 peak at 5570 ft registered a value of 10.45 mg HC/g rock which is inconsistent with the low thermal evolution of the O.M. in the samples, based on the values of TOC, S1 and bitumen extracted (EOM). The value of Tmax is proportional to the thermal maturity of the organic matter in a rock (Tissot and Welte 1984). Tmax values vary between 328 and 445 °C, with an average value of 417.5 °C (SD ± 26.23 °C), indicating rocks relatively immature or at the start of its early maturity.

Present-day hydrogen index (HIpd) suggests that a significant number of samples from the Tumaco-1-ST-P well corresponds to type II/III kerogen, characterized by HIpd between 300 and 600 mg HC/g TOC. This kind of kerogen is dominated by liptinitic macerals, despite a minor vitrinite and inertinite input. Type II/III kerogen describes mixtures of transitional marine and terrestrial organic matter. Figure 3 displays the hydrogen index (HIpd) versus oxygen index (OIpd) cross-plot to illustrate the quality and level of maturation of the studied samples. Results cover a broad range of maturity between oil-prone type II kerogen with HIpd of 525 mg HC/g TOC and dry gas-prone type IV kerogen with HIpd of 13 mg HC/g TOC values, indicating that the O.M. in study comes from a single and unique kerogen with a significant variation of the organic facies and paleodepositional environments.
Fig. 3

Modified van Krevelen diagram based on IH versus IO for Tumaco-ST-P well, Tumaco basin, Colombia. HI = (S2/TOC) × 100, OI = (S3/TOC) × 100

Figure 4 shows the cross-plot HIpd versus Tmax to correlate kerogen type and thermal maturity in terms of the degree of kerogen conversion, indicating that most of the samples show a Tmax < 430 °C and HIpd < 600 mg HC/g TOC confirming an immature O.M. and type III kerogen. Some specimens, however, show an O.M. with oil generation potential and type II and II/III kerogen. The pseudo van Krevelen diagram between S2 and TOCpd % indicating the type and quality of the kerogen in the rock samples is shown in Fig. 5 (Langford and Blanc-Valleron 1990). Thus, a large number of rocks and cuttings from Tumaco-1-ST-P well confirm a type III and/or IV kerogen (gas prone and dry gas prone, respectively). About 20 samples showed a transitional type II/III kerogen, which would generate oil/gas, and a smaller number of samples presented a type II kerogen (oil prone, usually marine). Thus, Cascajal and Tangareal del Mira formations show the lower quality due to its terrestrial origin and its diagenetic maturity.
Fig. 4

Kerogen type and thermal maturity using HI (mg HC/g TOC) versus Tmax (°C)

Fig. 5

Kerogen type (pseudo van Krevelen diagram) using S2 peak (mg HC/g rock) versus present-day TOC,  %

Figure 6 shows the paleoenvironmental evolution based on the lithology and stratigraphic analyses for Tumaco-1-ST-P well (ANH-Antek S.A.S 2013). Since the kerogen type is related to the original type of organic matter and its evolution and preservation over time, which is in turn associated with depositional environment and climate (Hall et al. 2016), the evaluation of depositional environment can be done through the TOC content and RE-pyrolysis data and indexes. Thus, the results discussed in Sect. 4.1 indicate that O.M. was deposited in a fluvio-deltaic and deltaic (upper delta plain/lower delta plain and prodelta) environment on siliciclastic lithofacies with organofacies characterized by input of higher plants, algae, and marine algae on a II/III kerogen type which is consistent with the depositional environment deduced from lithology and stratigraphic analysis.
Fig. 6

Lithology, paleoenvironment and stratigraphic correlation for Tumaco-1-ST-S and Tumaco-1-ST-P wells (ANH-Antek S.A. 2013)

Vitrinite reflectance and maceral analysis

Organic petrography is used almost systematically as a complement of the screening parameters (TOC, RE-Py, Fluorescence, etc.) to evaluate the O.M. type and the characteristics of the depositional environment, such as redox conditions (oxic/anoxic), energy level, microorganisms type, and additional data that allows the quantification of the thermal evolution of the O.M. Mean random Vitrinite reflectance (Rv,r) of the dispersed organic matter was measured on immersed oil and reported in this paper as Ro (Pawlewicz and Finn 2013). Additionally, the Rc was calculated from Tmax (Jarvie et al. 2001). Although this approach works better when Tmax is between 420 and 500 °C, it has been used in this study due to this conversion works marginally well for type III kerogen which includes the most of the analyzed samples. Fifty samples were selected through the stratigraphic column for Ro analysis in order to better understand its thermal maturity and hydrocarbons potential. The average Ro value was 0.4046 ± 0.065% indicating an immature O.M.

Macerals are the individual components of the kerogen that have petrographically and geochemically distinct properties and an independent assessment of the quality, quantity, and thermal maturity of organic matter (Hall et al. 2016). Vitrinite, liptinites, and inertinites were the most common maceral groups found in the dispersed organic matter in Tumaco-1-ST-P samples, which in turn allow to identify the following maceral types: esporinite, cutinite, resinite, alginite, colotelinite, colodetrinite, funginite, exsudinite, exsudatinite, inertodetrinite, among others as is shown in the photomicrographs of Fig. 7. The origin of macerals identified has a resin of higher plants, spores/pollen, cuticular plants, algae, and mixtures of the above. These macerals come from type II kerogen, while the vitrinite identified in relatively high concentration comes from type III kerogen and probably originated from tissues of wood and other vegetables. The inertinite that groups types of macerals as nertodecrinite, fusinite, etc., could originate from wood carbonized fragments. The petrographic analysis indicates that the rocks studied are in immature state. Figure 8 shows the plot of depth (ft) versus Ro (%) for modeling of the evolution of the thermal maturity. However, rocks with O.M. in the hydrocarbon generation window can exist at 1700 ft in stratigraphic column between 950 and 11,900 ft
Fig. 7

Photomicrograph in reflected light and fluorescent (× 50) of sample T-11570. a Grains of vitrinite with different thermal maturities. b Inertinite and exudatinite, and c inertinite with exudatinite

Fig. 8

Linear regression of depth versus Ro (%) with confidence bounds of 95%, showing the depth up to approximately 17,000 feet (ellipse) where is expecting that the potential source rock will enter into the generation window for Tumaco Basin, Colombia

The variation of Ro with depth and the petrographic analysis indicates that almost all samples in the Tumaco-1-ST-P well are in the immature state where samples from Cascajal and Tangareal del Mira Fms show the lowest maturity, while the highest maturities were found in the Tumaco Fm. suggesting a consistent light increment of maturity with depth. This linear regression with confidence bounds of 95%, suggests a depth range up to approximately 17,000 feet (see ellipse) where it is expecting that the potential source rock will enter into the generation window for Tumaco Basin, Colombia.

To estimate the extension of the petroleum-generation process and the total generative capacity in an already mature source rock, information on the TOC and HI of organic matter prior to the onset of hydrocarbon generation is required (Jarvie 2012, Hall et al. 2016). Although TOCpd and HIpd classified the organic matter deposited in Tumaco 1-ST-P as immature for what one could assume that HIpd should be equal HIo (Jarvie 2012), we have used KinEx source rock modeling software (www.zetaware.com) to calculate the original TOC and HI based on present-day analyses (Table 1). The minimum differences in the original and present-day TOC and HI confirm that the O.M. in Tumaco-1-ST-P is very immature and that the data could be used to calibrate the maturity in the basin (Jarvie 2012). On average, the HIo (117.57 mg HC/g TOC) differs from HIpd (109.85 mg HC/g TOC) and is about 7.72 mg HC/g TOC confirming an immature stage of the O.M. in the sample rocks.

Figure 9 presents an idealized geochemical logging based on screening values (TOC and RE-Py) and the experimental vitrinite reflectance (Ro) associated with lithofacies, stratigraphic units and the age for Tumaco-1-ST-P well applying the molecular stratigraphy concepts, which allows observing the changes of organic facies that occur laterally or vertically into the column (Demaison in Peters 1986; Espitalié et al. 1987; Burwood et al. 1990; Peter et al. 2005). Tmax and Ro increase consistently with increasing depth and maturity; HIpd shows a few variation with depth in Tumaco Fm, except in the deepest interval where it is consistent with TOCpd contents, indicating a few kerogen conversion to petroleum or gas (low transformation ratios values).
Fig. 9

Idealized geochemical logging based on RE-pyrolysis indexes, TOC and Ro for Tumaco-ST-P, Tumaco basin, Colombia (modified from J.G. Demaison in Peters 1986). Ro is experimental vitrinite reflectance

Bitumen extracts and SARA fractionation

Table 1 also displays organic geochemical characteristics based on EOM  %, SARA, and GC/FID analysis of the bitumen extracted. The EOM is very low, ranging between 0.0018 and 0.75%, being the deepest units of the Tumaco-1-ST-P well (11,650 ft) which contains the largest concentrations. Thus, the EOM values characterize the Cascajal and Tangareal del Mira formations as poor, while Tumaco Fm varies between fair and good quality (Bacon et al. 2000). The quantity and composition of the bitumen extracted depend on the original organic matter, organic facies, depositional environment, thermal maturity, and the extension of the expulsion and could also reflect contamination by drilling mud/fluids or migration of hydrocarbons. These last two events are discarded in Tumaco-1-ST-P well due to the low amount of O.M. extracted.

SARA fractionation shows the highest values for the resin fractions (NSO compounds), in most of the organic extracts, varying between 17.47 and 62.33%. Asphaltene fractions vary between 4.65 and 59.02%, and the aromatic fractions range between 0.1 and 21.28%. Finally, the fraction of saturated hydrocarbons varies between 4.99 and 43.81%. Tissot and Welte (1984) proposed a ternary diagram to identify the organic matter type based on the SARA fractionation. Thus, Tumaco-1-ST-P well samples classify as naphthenic bitumen due to its high resin and asphaltene concentrations. The SARA analysis shows a relatively low dispersion on its fraction, indicating that this bitumen has the same source and origin. The saturate/aromatic ratios are in all samples very high, except in the sample T2928 (0.29%). Thus, the SAT/ARO ratio indicates a very low content of aromatic hydrocarbons in the entire column and limits the use of the aromatic fraction as maturity indicator as it will be discussed later in Sect. 4.4.2.1.

Source and depositional environment

n-alkanes and isoprenoids

Gas chromatographic profiles of selected crude oils are shown in Fig. 10. The geochemical ratios based on n-alkanes distribution are displayed in Table 2. In general, the n-alkanes are the most abundant components in the saturate fraction for all samples (range 4.39–43.81%) although as stated above saturated hydrocarbons are the major fraction of the bitumen extract. Bitumen extracts have a n-alkanes distribution between n-C10 and n-C33, with bimodal distribution and maximum between n-C15 and n-C17, indicating an algal/microbial input and n-C25 to n-C27, showing a significant input of terrigenous organic matter, suggesting that this O.M. was originated from a type II/III or III kerogen. A dominance of n-alkanes around of n-C17 is thus interpreted as an indication of a marine source (Jones 1986). The GC profiles for samples T5509 and T-8243 show a special characteristic associated with the presence of high concentration of unknown organic compounds around n-C29 to n-C31 and related to recent O.M. (immature) in a process of decomposition and consistent with the concept that many of these samples are in an early diagenetic stage.
Fig. 10

GC/FID C15+ chromatograms of saturate fractions of selected rock extracts in the Tumaco-1-ST-P, Tumaco basin, Colombia

Table 2

Geochemical ratios based on SARA fractionation and GC/FID analyses of the organic extracts from rocks and cuttings in Tumaco-1-ST-P, Tumaco basin, Colombia

Sample I.D.

Depth (Ft)

Estrat. unit

Lithology

EOM (%)

SAT (%)

ARO (%)

RES (%)

ASP (%)

CPI

Pr/Ph

Pr/n-C17

Ph/n-C18

TAR

T-1130

1130

Cascajal Fm

Siltstone

0.0571

33.45

4.78

37.03

24.74

1.59

1.48

1.03

0.49

0.76

T-1190

1190

Cascajal Fm

Sandstone

0.0500

33.32

5.31

22.69

38.68

1.20

1.98

0.65

0.22

0.65

T-1290

1290

Cascajal Fm

Siltstone

0.0048

12.60

6.87

59.54

20.99

1.71

1.28

0.89

0.53

2.16

T-2490

2490

Tangareal de Mira Fm

Sandstone

0.0261

14.71

0.34

17.66

67.29

2.15

1.23

0.72

0.45

1.36

T-2550

2550

Tangareal de Mira Fm

Calcareous siltstone

0.0381

20.92

10.89

39.21

28.98

1.36

1.53

0.76

0.41

0.28

T-2570

2570

Tangareal de Mira Fm

Sandstone

0.0368

34.28

2.68

35.34

27.70

1.69

1.26

0.77

0.50

0.67

T-2590

2590

Tangareal de Mira Fm

Sandstone

0.0234

18.24

3.20

51.51

27.05

1.23

1.21

0.78

0.46

0.12

T-2610

2610

Tangareal de Mira Fm

Calcareous sandstone

0.1790

5.67

1.89

47.26

45.18

3.41

0.44

0.64

1.38

1.15

T-4130

4130

Tangareal de Mira Fm

Sandstone

0.0431

15.78

2.52

41.86

39.84

1.51

1.20

0.75

0.63

0.40

T-4330

4330

Tangareal de Mira Fm

Calcareous siltstone

0.0451

20.26

2.67

40.73

36.34

3.41

0.44

0.64

1.38

1.15

T-4410

4410

Tangareal de Mira Fm

Calcareous sandstone

0.0636

22.09

2.97

36.18

38.76

2.64

0.50

0.80

1.58

0.97

T-4470

4470

Tangareal de Mira Fm

Calcareous sandstone

0.0692

15.14

3.29

32.26

49.31

2.80

0.52

0.80

1.37

1.16

T-5030

5030

Tangareal de Mira Fm

Calcareous sandstone

0.0277

17.92

4.02

38.92

39.14

1.47

1.31

1.64

1.16

0.51

T-5394

5394

Tangareal de Mira Fm

Calcareous mudstone

0.0054

42.99

6.79

27.14

23.08

3.21

0.37

1.21

1.25

Biod.

T-5475

5475

Tumaco Fm

Mudstone

0.0290

15.76

3.07

48.80

32.37

1.24

0.75

2.06

2.44

1.33

T-5509

5509

Tumaco Fm

Calcareous mudstone

0.0900

16.86

2.35

38.26

42.53

1.80

0.34

3.07

10.93

3.53

T-5560

5560

Tumaco Fm

Calcareous siltstone

0.0112

15.17

6.25

48.18

30.40

0.47

0.47

1.92

2.67

1.00

T-5570

5570

Tumaco Fm

Calcareous sandstone

0.0744

25.87

3.59

37.72

32.82

1.46

1.07

0.78

0.64

0.30

T-5650

5650

Tumaco Fm

Calcareous siltstone

0.0080

18.68

2.67

60.05

18.60

1.48

1.15

0.69

0.45

0.09

T-5750

5750

Tumaco Fm

Calcareous siltstone

0.0267

16.74

3.54

53.05

26.67

1.43

1.01

0.53

0.45

0.25

T-5810

5810

Tumaco Fm

Siltstone

0.0159

19.35

3.63

59.85

17.17

1.17

1.20

0.72

0.58

0.11

T-5890

5890

Tumaco Fm

Calcareous siltstone

0.0433

16.33

3.16

51.60

28.91

1.45

1.30

0.75

0.55

0.15

T-5910

5910

Tumaco Fm

Siltstone

0.0106

24.31

4.05

42.55

29.09

1.47

1.34

0.77

0.52

0.22

T-5950

5950

Tumaco Fm

Calcareous siltstone

0.0181

16.47

4.11

52.11

27.31

1.41

1.42

0.87

0.58

0.66

T-5990

5990

Tumaco Fm

Calcareous siltstone

0.0120

11.21

3.06

47.37

38.37

1.47

1.22

0.88

2.08

0.47

T-6010

6010

Tumaco Fm

Siltstone

0.0084

21.34

4.93

47.61

26.12

1.54

1.19

0.84

1.56

1.04

T-6070

6070

Tumaco Fm

Calcareous sandstone

0.0214

17.45

2.68

57.69

22.18

1.76

1.16

1.02

0.86

2.36

T-6090

6090

Tumaco Fm

Calcareous siltstone

0.0060

31.91

7.09

44.33

16.67

2.23

0.65

1.16

2.28

3.88

T-6110

6110

Tumaco Fm

Calcareous sandstone

0.0065

20.81

6.94

53.50

18.75

1.32

1.23

0.72

0.95

0.77

T-6130

6130

Tumaco Fm

Calcareous sandstone

0.1500

7.98

2.13

33.54

56.35

1.16

1.56

0.87

1.13

1.35

T-6150

6150

Tumaco Fm

Siltstone

0.1350

6.99

1.75

26.23

65.03

1.41

0.90

0.95

2.54

0.37

T-6170

6170

Tumaco Fm

Calcareous sandstone

0.0145

18.24

3.77

54.08

23.91

2.80

0.99

1.00

2.33

2.09

T-6190

6190

Tumaco Fm

Siltstone

0.1020

8.80

1.04

22.79

67.37

1.79

0.84

1.03

2.51

0.68

T-6210

6210

Tumaco Fm

Calcareous siltstone

0.0264

11.50

2.60

46.76

39.14

2.98

1.19

0.82

0.59

1.60

T-6250

6250

Tumaco Fm

Calcareous siltstone

0.0301

13.05

2.70

62.10

22.15

1.30

1.19

0.74

0.50

0.51

T-6310

6310

Tumaco Fm

Calcareous sandstone

0.0185

10.91

2.60

55.06

31.43

1.11

1.39

0.72

0.40

1.16

T-6390

6390

Tumaco Fm

Calcareous sandstone

0.2750

12.10

1.34

27.54

59.02

1.65

1.15

0.63

0.38

0.08

T-6430

6430

Tumaco Fm

Sandstone

0.0123

19.46

4.32

48.11

28.11

1.34

1.23

0.68

0.45

0.22

T-6550

6550

Tumaco Fm

Sandstone

0.0106

16.24

3.75

51.20

28.81

1.41

1.23

0.69

0.41

0.23

T-6570

6570

Tumaco Fm

Sandstone

0.1580

8.68

0.12

29.05

62.15

1.25

1.11

0.69

0.42

0.28

T-6590

6590

Tumaco Fm

Siltstone

0.0919

8.64

1.73

29.82

59.81

1.31

1.27

0.72

0.41

0.34

T-6630

6630

Tumaco Fm

Siltstone

0.0427

4.34

0.96

18.33

76.37

1.06

1.06

0.74

0.49

0.39

T-6710

6710

Tumaco Fm

Calcareous siltstone

0.0177

18.60

3.95

56.35

21.10

1.62

1.23

0.92

0.67

0.72

T-6750

6750

Tumaco Fm

Sandstone

0.0168

20.96

3.97

49.85

25.22

1.38

1.22

0.85

0.55

0.82

T-6770

6770

Tumaco Fm

Calcareous siltstone

0.0165

23.19

4.00

58.36

14.45

1.50

1.40

0.82

0.57

1.02

T-6790

6790

Tumaco Fm

Calcareous sandstone

0.2440

10.55

0.13

27.31

62.01

1.90

1.12

1.03

0.77

0.26

T-6810

6810

Tumaco Fm

Calcareous sandstone

0.0169

14.75

2.11

61.10

22.04

1.66

1.31

1.06

0.80

0.67

T-6830

6830

Tumaco Fm

Calcareous sandstone

0.0142

18.83

5.94

58.45

16.78

1.75

1.34

0.95

0.69

0.82

T-6850

6850

Tumaco Fm

Calcareous sandstone

0.0199

36.17

4.91

39.75

19.17

2.09

1.27

0.94

0.71

0.91

T-6890

6890

Tumaco Fm

Siltstone

0.0134

21.69

5.21

59.00

14.10

1.91

1.33

0.94

0.72

0.94

T-7011

7050

Tumaco Fm

Calcareous mudstone

0.0165

10.35

2.07

70.39

17.19

1.32

1.19

1.04

0.62

0.52

T-7043

7110

Tumaco Fm

Siltstone

0.0988

16.70

0.25

20.02

63.03

1.66

1.18

0.80

0.48

0.53

T-7130

7130

Tumaco Fm

Calcareous sandstone

0.0036

27.10

2.46

41.87

28.57

1.68

1.34

1.08

0.72

0.19

T-7210

7210

Tumaco Fm

Calcareous sandstone

0.0091

19.77

4.24

53.65

22.34

1.29

1.09

1.02

0.51

0.26

T-7230

7230

Tumaco Fm

Calcareous siltstone

0.0018

22.67

0.00

62.33

15.00

0.92

0.85

1.00

0.53

0.18

T-7290

7290

Tumaco Fm

Calcareous siltstone

0.0039

36.62

6.86

43.48

13.04

1.12

1.27

0.77

0.58

0.13

T-7310

7310

Tumaco Fm

Calcareous siltstone

0.0203

18.36

3.82

42.84

34.98

1.31

1.32

0.72

0.59

0.50

T-7330

7330

Tumaco Fm

Calcareous siltstone

0.0068

28.72

4.31

38.76

28.21

1.09

1.47

0.66

0.50

1.13

T-7450

7450

Tumaco Fm

Calcareous siltstone

0.0064

26.92

6.33

45.92

20.83

1.76

0.79

0.93

0.67

2.27

T-7470

7470

Tumaco Fm

Siltstone

0.0182

30.98

1.72

29.26

38.04

1.16

0.90

0.87

0.59

1.28

T-7591

7591

Tumaco Fm

Siltstone

0.0129

30.24

13.23

25.82

30.71

0.69

1.27

2.07

1.54

0.28

T-7693

7693

Tumaco Fm

Calcareous mudstone

0.0156

18.33

5.87

46.19

29.61

5.32

1.69

1.78

1.41

3.28

T-7712

7712

Tumaco Fm

Calcareous mudstone

0.1620

10.64

0.47

32.28

56.61

2.60

1.36

1.56

1.43

4.67

T-7777

7777

Tumaco Fm

Calcareous mudstone

0.0080

23.87

7.02

46.33

22.78

4.80

0.67

2.28

2.29

13.40

T-7861

7861

Tumaco Fm

Calcareous siltstone

0.0190

43.81

6.92

36.13

13.14

3.33

1.13

3.05

2.97

4.89

T-7895

7895

Tumaco Fm

Calcareous siltstone

0.0192

18.19

7.28

48.51

26.02

4.46

2.32

3.63

1.96

10.53

T-7911

7911

Tumaco Fm

Calcareous siltstone

0.0113

20.17

6.37

52.03

21.43

1.07

3.00

2.62

1.10

0.37

T-7928

7928

Tumaco Fm

Sandstone

0.1870

6.12

21.28

17.31

55.29

4.25

1.35

5.74

4.88

16.17

T-8084

8084

Tumaco Fm

Siltstone

0.1580

10.11

0.22

31.94

57.73

1.45

1.20

1.60

0.86

0.83

T-8145

8145

Tumaco Fm

Siltstone

0.0140

17.02

3.65

21.88

57.45

1.17

1.02

1.27

0.68

Biod.

T-8211

8211

Tumaco Fm

Mudstone

0.0089

23.29

6.47

50.47

19.77

2.02

1.54

4.31

2.95

3.16

T-8233

8233

Tumaco Fm

Calcareous mudstone

0.0047

26.39

7.20

45.58

20.83

0.84

1.74

2.11

1.05

0.32

T-8243

8243

Tumaco Fm

Calcareous mudstone

0.0326

22.55

8.46

37.84

31.15

6.73

1.64

5.17

2.88

15.85

T-8255.5

8255.5

Tumaco Fm

Calcareous mudstone

0.0604

31.74

5.29

25.92

37.05

5.46

1.80

2.77

1.91

11.60

T-8275

8275

Tumaco Fm

Calcareous siltstone

0.0229

28.25

6.52

46.73

18.50

4.74

1.98

3.95

2.72

9.02

T-8302.5

8302.5

Tumaco Fm

Siltstone

0.0141

15.90

11.48

43.27

29.35

2.98

2.29

3.90

2.25

6.14

T-8312.5

8312.5

Tumaco Fm

Siltstone

0.0130

11.94

9.18

57.83

21.05

2.45

1.88

3.68

3.01

5.65

T-8317

8317

Tumaco Fm

Calcareous siltstone

0.0040

4.99

4.98

59.80

30.23

0.88

1.78

1.38

0.60

0.50

T-8332.5

8332.5

Tumaco Fm

Siltstone

0.0088

15.11

10.07

56.64

18.18

4.21

1.73

2.91

1.36

6.02

T-8338

8338

Tumaco Fm

Mudstone

0.0244

28.35

5.00

38.35

28.30

4.00

1.50

4.27

2.74

12.09

T-8354.5

8354.5

Tumaco Fm

Calcareous siltstone

0.0184

12.77

6.96

59.77

20.50

3.07

1.79

4.27

2.93

7.43

T-8370.5

8370.5

Tumaco Fm

Siltstone

0.0142

25.17

10.90

42.78

21.15

3.05

2.34

2.49

1.16

5.50

T-8380

8380

Tumaco Fm

Siltstone

0.0205

15.70

9.56

52.57

22.17

3.62

2.44

4.82

2.49

11.28

T-8431

8431

Tumaco Fm

Siltstone

0.0316

5.89

4.81

37.45

51.85

1.04

2.72

2.75

1.33

1.44

T-8448

8448

Tumaco Fm

Siltstone

0.0122

27.78

7.71

47.06

17.45

2.56

2.48

3.14

1.56

5.83

T-8850

8850

Tumaco Fm

Siltstone

0.0079

13.94

11.15

52.96

21.95

1.40

1.62

1.03

0.52

1.47

T-8870

8870

Tumaco Fm

Calcareous sandstone

0.0100

26.57

5.31

46.76

21.36

1.99

1.98

0.97

0.48

0.62

T-8890

8890

Tumaco Fm

Calcareous sandstone

0.2480

11.90

3.04

29.15

55.91

0.82

1.39

0.81

0.48

0.15

T-9150

9150

Tumaco Fm

Calcareous siltstone

0.0090

27.08

7.39

50.48

15.05

1.44

1.31

1.44

1.05

0.80

T-9790

9790

Tumaco Fm

Calcareous sandstone

0.0165

31.73

5.40

42.53

20.34

1.68

1.49

1.30

1.03

0.91

T-10079

10,079

Tumaco Fm

Mudstone

0.0401

25.01

3.70

30.41

40.88

1.78

1.02

4.01

3.43

2.00

T-11610

11,610

Tumaco Fm

Calcareous siltstone

0.2120

20.91

5.07

32.31

41.71

1.17

1.66

0.87

0.47

0.18

T-11650

11650

Tumaco Fm

Calcareous siltstone

0.7900

19.87

2.28

42.33

35.52

0.97

1.48

0.79

0.48

0.05

T-11670

11,670

Tumaco Fm

Calcareous sandstone

0.0793

18.17

3.05

45.59

33.19

1.22

1.47

0.91

0.54

0.26

T-11690

11,690

Tumaco Fm

Calcareous siltstone

0.0399

13.15

2.19

32.88

51.78

1.16

1.39

1.02

0.44

0.20

T-11710

11,710

Tumaco Fm

Calcareous siltstone

0.7200

23.40

2.27

24.53

49.80

0.68

1.38

0.83

0.50

0.06

T-11730

11,730

Tumaco Fm

Calcareous siltstone

0.2470

26.40

4.20

33.18

36.22

0.93

1.41

0.80

0.50

0.16

T-11790

11,790

Tumaco Fm

Calcareous siltstone

0.1340

21.43

2.65

33.48

42.44

1.02

1.29

0.85

0.51

0.20

T-11810

11,810

Tumaco Fm

Calcareous siltstone

0.0743

29.87

2.99

33.42

33.72

1.02

1.36

0.90

0.53

0.13

T-11870

11,870

Tumaco Fm

Calcareous siltstone

0.1280

35.89

4.20

55.26

4.65

0.84

1.40

0.78

0.48

0.06

EOM, extractable organic matter; CPI, carbon preference index = [(n-C25 + n-C27 + n-C29 + n-C31 + n-C33/n-C24 + n-C26 + n-C28 + n-C30 + n-C32) + (n-C25 + n-C27 + n-C29 + n-C31 + n-C33/n-C26 + n-C28 + n-C30 + n-C32 + n-C34)]/2; Pr/Ph, pristane/phytane; Pr/n-C17, pristane/n-C17; Ph/n-C18, phytane/n-C18; TAR, terrestrial/aquatic O.M. ratio = n-C27 + n-C29 + n-C31/n-C15 + n-C17 + n-C19; Biod., biodegraded

A marine-deltaic transitional environment has been strongly supported by the geological model proposed in the original ANH-Antek technical report (ANH-Antek S.A. 2013). The terrestrial origin of a large part of the organic extracts studied comes from the epicuticular wax high plants, which presents a wide distribution of n-alkanes with a marked predominance of hydrocarbons with odd number of carbon atoms (n-C25, n-C27, n-C29, n-C31); while samples of marine origin located more toward the bottom and in the deepest part of the column have a significant bacterial, algal, and phytoplanktonic contribution, characterized by a predominance of heptadecane (n-C17). Some of the chromatographic profiles allow observing a hump or the so-called unresolved complex mixture (UCM), which confirms that different levels of diagenetic biodegradation are in progress in the basin.

The Pr/Ph ratio in Tumaco-1-ST-P displays values below 3.0, although most of the samples fall between 1.0 and 1.5, which indicates that these samples were deposited in a suboxic to oxic environment and were derived from marine shales. There are some samples with values of Pr/Ph ratio < 1.0, suggesting a more carbonatic bitumen. Bitumen and crude oils derived from marine shale have a CPI values ranging from low to moderate (1.0–3.0), while those derived from source rocks containing mainly terrestrial O.M. present Pr/Ph ratios between 3.0 and 10. Carbonate rocks show Pr/Ph < 1.0 (Didyk et al. 1978). When the Pr/Ph is used as an indicator of redox conditions, a value < 3.0 for the organic extracts of the Tumaco-1-ST-P well, indicates that this O.M. was generated under suboxic–oxic conditions. According to Didyk et al. 1978, Pr/Ph < 1 in bitumen and crude indicates an environment at anoxic depositional environment, while Pr/Ph > 1 indicates an oxic deposition. In Tumaco-1-ST-P rocks, the Pr/Ph ratios display values below 3.0, with a high population of data ranging between 1.0 and 1.5, suggesting that these samples were deposited in a suboxic to an oxic environment.

The n-alkanes/isoprenoids ratios (Pr/n-C17 and Ph/n-C18) decrease with the maturity since more n-alkanes are released from kerogen by cracking (Tissot et al. 1971) and are more thermally stable than isoprenoids. Figure 11 shows that most of the samples in Tumaco-1-ST-P well have been originated from type II-III kerogen (transitional marine-terrestrial) and type III kerogen (terrestrial), although a few samples from Tangareal del Mira and Tumaco formations seem to have been originated from a type II kerogen (marine). Thus, Pr/n-C17 varies between 0.53 and 5.74 and Ph/n-C18 ranging between 0.22 and 4.88, suggesting a broad range of maturities and biodegradation processes and a depositional environment from suboxic to oxic characteristics.
Fig. 11

Geochemical correlation between Isoprenoids/n-alkanes showing the sources and depositional environment of the organic matter in the Tumaco-1-ST-P, Tumaco basin, Colombia

The carbon preference index (CPI) relates the odd/even hydrocarbon predominance (Bray and Evans 1961). Immature rocks with a significant contribution of superior plants are dominated by odd n-alkanes, especially n-C27, n-C29 and n-C31. These n-alkanes are originated from the epicuticular waxy (plant leaves) and are synthesized directly by plants or by defunctionalization from alcohols, acids or esters, in whose case, the CPI values will be > 1.0. n-alkanes derived from marine O.M. tend to have a small or not marked CPI. Regarding to hypersaline carbonates or evaporitic rocks, CPI presents a slight pair preference of numbers of carbon. In all cases, the CPI decreases with the maturity of the O.M. This is due to a geochemical process that combines the n-alkanes generation from the kerogen and derived from different biological precursors and thermal cracking of hydrocarbons in the early diagenesis. The CPI values found in Tumaco-1-ST-P well present a wide dispersion ranging between 0.47 and 6.73, with a high amount of CPI values ranging between 1 and 3 and a few number of samples (< 6%) with CPI < 1.0. High values of CPI indicate low maturity and terrestrial origin, bitumen with CPI around 1 originating from marine contributions. Samples from Cascajal Fm present CPI values ranging between 1.20 and 1.71 indicating a marine-deltaic transitional O.M. source located in a paleoenvironment of deltaic plain highly immature. The Tangareal del Mira bitumen presents CPI in the range between 1.23 and 3.41 confirming a transitional marine-deltaic depositional environment, while the Tumaco Fm maintains the same marine-deltaic influence of the previous formation up to a depth of approximately 8000 ft, from which up to 12,000 ft, becomes a paleoenvironment with a tendency to the marine platform (shelf marine).

The vertical distribution of terrestrial/aquatic O.M. ratio (TAR) values is relevant to determine the relative changes in the contribution of the terrestrial versus aquatic O.M. over the time, particularly considering recent sediments (Meyers 1997). TAR displays values varying between 0.05 and 16.17 (average 2.18), which confirms the constant variations of organic facies from algal/bacterial and/or land origin through the stratigraphic column. High TAR values in recent sediment extracts, as in the case of Tumaco-1-ST-P, indicate a great contribution by land plants that aquatic to the depositary environment (Bourbonniere and Meyers 1996, cited by Peter et al. 2005). This ratio should be used with care since it is susceptible to drastic changes by effects of maturation and biodegradation.

Terpanes and steranes

The biological markers were identified based on full-scan GC/MS analysis, comparing the mass fragmentograms of the specific biomarkers with data previously reported (Philp 1985; Wang 1993; Peter et al. 2005) and with bitumen and crude oils of known composition (e.g., NGS NSO-1 oil sample, NPD-Nigoga; Boscan crude oil, Venezuela; Cauca/Patia and Buenaventura rock extracts, Colombia) (NPD-Nigoga 2000; Antek S.A. 2011).

Figure 12 (on the left) shows the tri-, tetra-, and pentacyclic terpane mass fragmentograms (m/z 191) and steranes (m/z 217) (on the right) for Tumaco-1-ST-P selected samples, while Table 3 displays the main geochemical correlation from terpane and sterane results. The terpane chromatographic profiles exhibit a particular features such as that the C30αβ(H)-hopane is the biggest terpane; the tricyclic terpane fraction extends from C19/3 until C30/3-R/S, Ts < Tm; the oleanane and gammacerane are present in medium to high concentrations; homohopanes are present in relatively low concentration and in some samples do not exist. When they are present, are distributed between C31 and C35, decreasing in the order C31 > C32 > C33 > C34 > C35-R/S.
Fig. 12

Mass fragmentograms showing the terpane (m/z 191) and sterane (m/z 217) distribution in Tumaco-1-ST-P well, Tumaco basin, Colombia

Table 3

Geochemical ratios based on terpanes (m/z 191 and 177) and steranes (m/z 217 and 218) in organic extracts from rocks and cuttings in Tumaco-1-ST-P, Tumaco basin, Colombia

Sample I.D.

HOAPNES, m/z 191 and m/z 177

TT19/TT23

TT21/TT23

TT23/H30

TTe24/H30

TT25/TT26

Ts/(Ts + Tm)

M30/H30

O. I.

G. I.

HH32 I. I.

HH32. H.I.

TT/TP

BNH Index

T-1130

0.80

0.60

2.40

0.28

1.18

0.18

0.47

8.99

36.86

0.51

19.12

2.20

11.40

T-1190

1.10

0.87

0.54

0.15

1.16

0.52

0.18

7.16

5.62

0.55

22.40

1.03

11.08

T-1290

0.16

0.49

0.25

0.10

1.10

0.54

0.27

6.45

16.30

0.56

22.51

0.54

6.34

T-2490

0.23

0.58

2.06

0.32

1.76

0.37

0.96

15.59

Biod.

0.51

Biod.

1.50

8.54

T-2550

0.22

0.56

1.78

0.23

1.67

0.43

0.65

12.03

53.56

0.55

18.84

1.63

3.93

T-2570

0.06

0.57

2.23

0.24

1.67

0.48

0.57

10.47

50.91

0.55

19.69

1.85

3.82

T-2590

0.09

0.48

1.90

0.25

1.77

0.52

0.66

12.58

70.97

0.56

18.99

1.60

2.92

T-2610

0.37

0.76

0.82

0.26

1.40

0.52

1.25

18.54

Biod.

0.43

Biod.

0.60

6.72

T-4130

0.58

0.95

0.84

0.20

1.48

0.41

1.47

11.20

Biod.

0.52

Biod.

1.26

1.86

T-4330

0.26

0.84

1.06

0.18

1.53

0.53

1.96

23.65

Biod.

0.57

Biod.

1.26

9.17

T-4410

0.38

1.01

0.71

0.21

1.73

0.48

1.83

26.84

Biod.

0.54

Biod.

0.99

7.13

T-4470

0.31

0.82

0.68

0.19

1.81

0.42

1.73

21.90

Biod.

0.49

Biod.

0.92

5.05

T-5030

0.22

0.51

0.30

0.10

1.27

0.51

0.11

8.17

3.75

0.59

24.56

0.57

1.53

T-5394

0.11

0.72

0.89

0.20

1.33

0.35

1.40

36.30

Biod.

0.59

Biod.

1.03

71.57

T-5475

0.24

0.59

0.13

0.06

1.85

0.51

0.81

9.04

Biod.

0.64

Biod.

0.68

7.97

T-5509

0.36

0.74

0.12

0.07

2.27

0.33

2.23

19.34

Biod.

0.60

Biod.

0.41

17.87

T-5560

0.12

1.55

0.28

0.10

2.08

0.74

1.87

24.53

Biod.

0.28

Biod.

0.68

11.85

T-5570

0.16

0.69

0.93

0.12

2.50

0.53

0.42

11.11

50.61

0.56

19.00

1.05

57.53

T-5650

0.32

0.87

2.23

0.34

2.01

0.63

0.45

11.05

52.97

0.55

23.02

2.56

21.07

T-5750

0.20

0.77

2.19

0.23

2.43

0.63

0.68

14.92

96.14

0.58

Biod.

1.90

3.35

T-5810

0.29

0.84

2.04

0.21

2.10

0.64

0.82

15.85

Biod.

0.56

Biod.

1.18

86.78

T-5890

0.33

0.87

2.18

0.25

2.34

0.64

0.83

15.39

Biod.

0.61

Biod.

1.56

Biod.

T-5910

0.38

0.92

1.93

0.27

1.91

0.58

0.68

9.80

99.37

0.56

Biod.

1.59

Biod.

T-5950

0.30

0.80

1.12

0.34

1.67

0.64

0.97

13.55

Biod.

0.55

Biod.

0.99

94.95

T-5990

0.51

0.77

0.73

0.32

1.51

0.58

0.90

16.27

Biod.

0.57

Biod.

0.72

65.18

T-6010

0.40

0.75

0.49

0.23

1.38

0.47

0.44

8.32

46.13

0.54

Biod.

0.86

20.54

T-6070

0.33

0.71

0.79

0.34

1.56

0.60

1.13

17.14

Biod.

0.51

Biod.

0.67

41.15

T-6090

0.36

0.80

0.68

0.38

1.79

0.59

1.08

14.96

Biod.

0.45

Biod.

0.65

Biod.

T-6110

0.54

0.66

0.66

0.36

1.08

0.20

0.34

13.40

36.37

0.54

Biod.

1.12

84.49

T-6130

0.56

0.75

0.55

0.28

1.37

0.40

0.43

8.38

46.85

0.55

Biod.

1.05

19.90

T-6150

0.41

0.75

0.85

0.36

1.72

0.61

1.08

15.63

Biod.

0.57

Biod.

0.68

Biod.

T-6170

0.44

0.74

0.74

0.35

1.42

0.52

0.92

17.65

Biod.

0.67

Biod.

0.59

70.44

T-6190

0.39

0.72

0.77

0.38

2.27

0.58

1.09

15.00

Biod.

0.39

Biod.

0.60

91.64

T-6210

0.21

0.64

1.70

0.28

2.01

0.52

1.06

15.99

Biod.

0.54

Biod.

1.29

41.06

T-6250

0.39

0.82

1.52

0.32

2.10

0.57

0.67

14.57

94.69

0.55

Biod.

1.39

75.42

T-6310

0.31

0.78

0.94

0.38

1.48

0.52

0.33

14.64

29.54

0.56

24.30

1.35

30.53

T-6390

0.22

0.77

1.35

0.30

1.73

0.52

0.32

8.34

28.30

0.55

Biod.

1.93

13.48

T-6430

0.25

0.86

2.08

0.37

2.04

0.55

0.45

14.48

55.75

0.56

Biod.

2.04

41.79

T-6550

0.38

0.78

1.21

0.37

1.68

0.55

0.53

12.67

76.32

0.57

Biod.

1.36

35.98

T-6570

0.25

0.74

1.23

0.35

1.87

0.58

0.55

13.09

77.43

0.56

Biod.

1.50

35.19

T-6590

0.22

0.72

1.08

0.38

1.63

0.56

0.36

12.22

39.81

0.53

Biod.

1.34

26.09

T-6630

0.32

0.77

1.04

0.33

1.53

0.54

0.37

9.62

44.23

0.58

Biod.

1.44

30.20

T-6710

0.46

0.81

0.61

0.20

1.49

0.61

0.88

12.82

Biod.

0.42

Biod.

0.96

21.63

T-6750

0.27

0.70

0.97

0.23

1.89

0.54

0.54

10.41

74.72

0.58

Biod.

1.10

36.77

T-6770

0.32

0.73

0.85

0.19

1.87

0.58

0.76

12.86

Biod.

0.75

Biod.

1.15

32.82

T-6790

0.30

0.76

6.76

2.07

1.58

0.64

9.63

Biod.

Biod.

0.51

Biod.

1.10

Biod.

T-6810

0.39

0.81

0.58

0.14

1.82

0.55

0.86

12.06

Biod.

0.41

Biod.

0.69

23.14

T-6830

0.34

0.87

0.49

0.16

1.76

0.54

0.77

9.64

Biod.

0.46

Biod.

0.73

18.10

T-6850

0.22

0.61

0.34

0.12

1.62

0.58

0.43

7.53

59.25

0.59

Biod.

0.65

28.52

T-6890

0.30

0.78

0.53

0.15

1.47

0.56

0.67

9.17

Biod.

0.74

Biod.

0.90

28.49

T-7050

0.26

0.75

0.76

0.25

1.44

0.51

0.68

13.36

99.60

0.69

Biod.

1.07

43.30

T-7110

0.28

0.72

0.42

0.17

1.35

0.49

0.36

6.52

37.92

0.83

Biod.

0.95

6.81

T-7130

0.34

0.76

0.58

0.26

1.27

0.53

0.57

10.62

86.35

0.71

Biod.

1.20

12.20

T-7210

0.39

0.75

0.44

0.24

1.37

0.50

0.68

9.94

Biod.

0.71

Biod.

0.96

10.58

T-7230

0.25

0.71

0.38

0.20

1.58

0.49

0.51

8.38

75.05

0.65

Biod.

0.87

7.71

T-7290

0.32

0.84

0.43

0.25

1.37

0.49

0.51

9.16

71.17

0.72

Biod.

0.95

16.85

T-7310

0.31

0.70

0.48

0.29

1.30

0.49

0.45

10.61

55.14

0.77

Biod.

0.96

19.04

T-7330

0.32

0.71

0.55

0.36

1.34

0.48

0.37

10.61

34.65

0.85

Biod.

1.04

11.82

T-7450

0.23

0.80

0.33

0.12

1.77

0.42

0.44

1.69

43.85

0.80

Biod.

0.77

11.80

T-7470

0.22

0.74

0.63

0.19

1.48

0.52

0.59

11.25

84.61

0.80

Biod.

1.04

12.71

T-7591

0.21

0.64

0.44

0.14

1.70

0.54

0.99

15.85

Biod.

0.55

Biod.

0.91

63.28

T-7693

0.16

0.59

0.65

0.16

2.11

0.16

0.66

21.80

87.48

0.66

Biod.

0.86

13.09

T-7712

0.16

1.49

0.63

0.22

1.80

0.49

1.00

16.50

Biod.

0.47

Biod.

1.20

60.72

T-7777

0.29

0.59

0.33

0.10

1.88

0.56

0.80

18.78

Biod.

0.44

Biod.

1.04

28.97

T-7861

0.25

0.54

0.33

0.15

1.53

0.30

1.08

29.49

Biod.

0.43

Biod.

0.91

13.89

T-7895

0.22

0.94

0.44

0.13

2.81

0.17

0.83

50.48

94.37

0.45

Biod.

0.71

Biod.

T-7911

0.18

0.63

1.75

0.44

2.29

0.26

1.05

68.86

80.20

0.40

Biod.

0.71

Biod.

T-7928

0.19

0.56

0.20

0.11

2.17

0.34

0.61

24.55

Biod.

0.44

Biod.

0.57

Biod.

T-8084

0.11

0.71

0.47

0.16

1.94

0.24

0.38

19.02

29.20

0.66

Biod.

0.93

Biod.

T-8145

0.09

0.61

0.78

0.18

1.82

0.28

0.37

44.00

20.92

0.83

Biod.

0.64

Biod.

T-8211

0.20

0.37

0.37

0.14

1.82

0.26

0.91

34.35

Biod

0.39

Biod.

0.69

Biod.

T-8233

0.20

0.95

0.79

0.23

2.42

0.21

0.80

96.51

Biod.

0.44

Biod.

1.38

Biod.

T-8243

0.22

0.45

0.21

0.09

2.45

0.16

0.59

68.70

99.03

0.31

Biod.

0.60

13.90

T-8255.5

0.17

0.53

0.51

0.14

1.82

0.11

0.81

79.98

Biod.

0.26

Biod.

0.71

14.23

T-8275

0.24

0.61

0.47

0.14

2.76

0.17

0.69

70.51

Biod.

0.33

Biod.

0.54

15.06

T-8302.5

0.16

0.31

0.50

0.41

Biod.

0.13

0.59

48.22

77.47

0.50

Biod.

1.97

Biod.

T-8312.5

0.20

0.49

0.29

0.12

Biod.

0.11

0.48

Biod.

92.02

0.47

Biod.

0.60

Biod.

T-8317

0.14

0.57

0.96

0.28

1.84

0.14

0.58

76.62

31.48

0.38

Biod.

0.76

Biod.

T-8332.5

0.22

0.57

0.37

0.12

2.14

0.07

0.42

69.84

68.53

0.36

Biod.

0.57

Biod.

T-8338

0.27

0.31

0.15

0.11

2.88

0.05

0.33

52.82

68.76

0.38

Biod.

0.55

Biod.

T-8354.5

0.19

0.31

0.19

0.11

2.58

0.07

0.52

40.39

64.61

0.40

Biod.

0.58

Biod.

T-8370.5

0.17

0.90

0.29

0.13

2.25

0.33

0.62

48.84

56.59

0.54

Biod.

0.70

Biod.

T-8380

0.20

0.44

0.32

0.14

1.93

0.31

0.90

71.52

Biod.

0.39

Biod.

0.63

22.82

T-8431

0.17

0.68

0.81

0.33

3.75

0.20

0.46

99.64

74.51

0.32

Biod.

0.51

Biod.

T-8448

0.17

0.78

0.21

0.10

4.76

0.26

0.29

56.13

39.74

0.19

Biod.

0.46

Biod.

T-8850

0.30

0.74

0.56

0.32

1.39

0.56

0.49

31.31

59.15

0.83

Biod.

0.59

89.83

T-8870

0.23

0.60

0.58

0.32

1.70

0.51

0.44

33.44

41.25

0.73

Biod.

0.55

Biod.

T-8890

0.23

1.62

0.11

0.06

1.10

0.02

0.27

1.36

30.78

0.56

Biod.

0.32

2.26

T-9150

0.29

0.74

0.35

0.21

1.20

0.52

0.68

16.86

88.36

0.60

Biod.

0.80

10.89

T-9790

0.34

0.70

0.27

0.13

1.52

0.46

0.47

39.76

49.47

0.71

Biod.

0.57

39.34

T-10079

0.29

0.72

0.12

0.06

1.01

0.12

0.55

47.98

43.74

0.71

Biod.

0.38

14.90

T-11610

0.36

1.52

0.12

0.07

1.29

0.03

0.28

1.61

28.93

0.56

Biod.

0.33

2.99

T-11650

0.28

1.62

0.10

0.06

1.04

0.03

0.28

1.14

31.62

0.55

Biod.

0.28

2.42

T-11670

0.24

1.59

0.09

0.06

1.13

0.05

0.28

1.95

34.20

0.55

Biod.

0.26

2.73

T-11690

0.31

0.86

0.29

0.18

1.42

0.48

0.42

19.22

32.19

0.68

Biod.

0.47

54.31

T-11710

0.21

1.53

0.12

0.07

1.06

0.03

0.26

1.16

28.65

0.56

Biod.

0.34

2.30

T-11730

0.30

1.54

0.12

0.06

1.10

0.06

0.27

1.51

28.96

0.55

Biod.

0.33

2.40

T-11790

0.26

1.38

0.12

0.06

1.24

0.05

0.26

2.12

29.67

0.54

Biod.

0.31

2.87

T-11810

0.30

1.47

0.14

0.06

1.21

0.06

0.26

2.41

28.03

0.54

Biod.

0.36

2.79

T-11870

0.33

0.12

0.16

0.07

1.25

0.06

0.26

1.82

28.30

0.55

Biod.

0.33

2.68

Sample I.D.

Steranes, m/z 217 and m/z 218

PREGIndex

C27ββS  %

C28ββS  %

C29ββS  %

C27ααR  %

C28ααR  %

C29ααR  %

C29αα (S/R)

C29αα S/S + R

C29 ββ/αα + ββ

C27Dia/C29αα-R

T-1130

40.36

27.97

31.41

40.62

27.54

25.23

47.23

0.37

0.27

0.40

1.69

T-1190

19.99

27.48

29.16

43.36

32.66

25.25

42.09

0.84

0.46

0.48

2.56

T-1290

18.41

28.34

41.53

30.13

31.08

26.43

42.49

0.73

0.42

0.39

1.65

T-2490

38.55

31.86

29.73

38.41

31.29

17.00

51.71

0.24

0.20

Biod.

1.24

T-2550

33.28

27.66

26.91

45.43

26.83

23.89

49.28

0.37

0.27

0.13

1.34

T-2570

34.97

25.45

27.81

46.74

22.33

23.61

54.06

0.35

0.26

0.14

1.46

T-2590

29.41

32.46

26.44

41.10

33.95

15.95

50.10

0.26

0.21

0.13

1.13

T-2610

15.97

24.16

44.19

31.65

33.23

19.91

46.85

0.05

0.05

0.02

Biod.

T-4130

34.15

26.12

31.64

42.24

46.03

18.77

35.21

0.14

0.12

0.33

0.42

T-4330

36.68

30.83

37.42

31.75

2.19

37.67

60.14

0.16

0.14

0.25

Biod.

T-4410

31.44

29.42

30.93

39.65

45.92

20.85

33.23

0.11

0.10

0.26

Biod.

T-4470

30.11

28.98

32.43

38.58

46.32

20.20

33.49

0.11

0.10

0.26

Biod.

T-5030

17.37

33.50

30.34

36.16

25.62

26.39

47.98

0.57

0.36

0.45

1.31

T-5394

Biod.

Biod.

Biod.

Biod.

40.87

18.30

40.83

0.03

0.03

0.25

Biod.

T-5475

20.37

43.92

34.40

21.68

50.95

16.26

32.79

0.15

0.13

0.18

Biod.

T-5509

14.00

41.27

36.13

22.60

49.27

21.63

29.10

0.09

0.08

0.21

Biod.

T-5560

16.34

39.75

36.76

23.49

42.60

25.49

31.91

0.07

0.06

0.25

Biod.

T-5570

25.72

40.15

40.89

18.96

37.94

26.31

35.75

0.41

0.29

0.32

0.85

T-5650

41.07

35.03

39.23

25.74

40.58

21.43

37.99

0.29

0.23

0.35

1.69

T-5750

36.78

33.94

37.58

28.48

37.46

21.72

40.82

0.14

0.12

0.30

0.71

T-5810

38.19

36.00

43.66

20.34

38.08

23.58

38.33

0.07

0.07

0.29

0.50

T-5890

42.91

41.06

43.23

15.71

38.26

22.81

38.93

0.09

0.08

0.32

0.47

T-5910

41.74

31.60

44.26

24.15

36.35

22.86

40.79

0.09

0.08

0.34

0.71

T-5950

36.44

28.08

47.26

24.66

38.71

22.70

38.59

0.07

0.07

0.30

0.61

T-5990

26.80

31.43

48.67

19.90

40.19

21.14

38.67

0.08

0.08

0.27

0.61

T-6010

27.30

33.66

45.83

20.51

34.53

24.54

40.93

0.25

0.20

0.32

1.19

T-6070

22.22

30.46

49.97

19.57

37.42

18.51

44.07

0.08

0.07

0.26

0.45

T-6090

26.17

22.21

50.45

27.34

40.66

19.35

39.98

0.06

0.06

0.29

0.51

T-6110

28.92

25.66

49.67

24.67

37.35

23.62

39.03

0.30

0.23

0.39

2.03

T-6130

30.87

25.67

43.83

30.50

37.37

23.84

38.79

0.27

0.22

0.34

1.52

T-6150

25.68

28.78

50.41

20.81

37.24

20.60

42.16

0.06

0.06

0.26

0.42

T-6170

23.29

35.52

52.66

11.82

33.21

20.04

46.75

0.06

0.06

0.26

0.48

T-6190

26.73

31.92

51.96

16.12

37.47

19.76

42.77

0.05

0.04

0.25

0.43

T-6210

29.76

37.56

38.30

24.15

32.19

18.65

49.15

0.11

0.10

0.26

0.50

T-6250

37.15

37.21

48.06

14.73

33.66

23.06

43.29

0.11

0.10

0.28

0.65

T-6310

34.39

35.03

41.24

23.73

29.24

25.64

45.12

0.33

0.25

Biod.

2.03

T-6390

40.47

34.05

45.59

20.36

39.57

21.87

38.56

0.32

0.24

0.34

1.41

T-6430

42.09

39.22

50.15

10.63

36.06

22.24

41.70

0.19

0.16

0.32

1.16

T-6550

35.39

38.93

51.18

9.88

34.61

25.94

39.45

0.14

0.12

0.29

0.95

T-6570

35.08

34.42

51.98

13.60

37.11

25.74

37.15

0.12

0.11

0.27

0.87

T-6590

35.69

32.64

45.76

21.60

38.03

23.25

38.72

0.27

0.21

0.35

2.07

T-6630

36.70

37.13

46.38

16.49

42.40

22.31

35.29

0.20

0.17

0.28

1.29

T-6710

23.66

39.38

46.15

14.47

37.02

22.80

40.18

0.05

0.04

0.26

0.35

T-6750

29.27

32.93

50.90

16.17

37.43

24.55

38.01

0.17

0.15

0.30

0.77

T-6770

25.71

26.59

53.76

19.65

36.73

23.47

39.80

0.08

0.07

0.28

0.46

T-6790

23.48

21.08

53.92

25.00

38.18

22.40

39.43

0.06

0.05

0.24

0.32

T-6810

19.73

24.94

57.53

17.53

36.22

23.45

40.33

0.06

0.06

0.24

0.24

T-6830

22.26

39.38

49.27

11.35

37.05

23.48

39.47

0.08

0.07

0.26

0.36

T-6850

13.51

35.74

46.15

18.12

33.61

24.49

41.90

0.24

0.19

0.37

1.18

T-6890

22.77

45.38

50.65

3.97

36.60

23.83

39.57

0.10

0.09

0.28

0.53

T-7050

31.10

42.01

47.34

10.65

38.33

23.13

38.55

0.21

0.18

0.29

0.81

T-7110

28.46

33.32

45.71

20.97

35.30

26.39

38.32

0.29

0.22

0.32

0.89

T-7130

30.67

33.24

50.17

16.59

42.63

22.75

34.62

0.17

0.15

0.30

0.84

T-7210

31.93

28.85

57.15

14.00

37.08

24.89

38.03

0.19

0.16

0.28

0.78

T-7230

28.08

26.02

51.37

22.61

40.60

23.80

35.60

0.17

0.14

0.27

0.81

T-7290

30.51

34.20

56.35

9.45

37.84

23.67

38.49

0.19

0.16

0.30

0.96

T-7310

30.44

37.99

46.26

15.75

36.08

24.58

39.33

0.29

0.22

0.30

1.61

T-7330

33.79

35.03

44.14

20.83

38.14

25.43

36.42

0.42

0.30

0.32

2.74

T-7450

26.28

31.19

52.47

16.34

32.76

27.15

40.10

0.23

0.19

0.31

0.67

T-7470

28.62

28.87

51.99

19.14

36.22

24.05

39.73

0.19

0.16

0.30

0.68

T-7591

Biod.

Biod.

Biod.

Biod.

23.97

14.89

61.14

0.03

0.03

0.24

Biod.

T-7693

Biod.

Biod.

Biod.

Biod.

20.87

19.54

59.58

0.01

0.01

0.29

Biod.

T-7712

Biod.

Biod.

Biod.

Biod.

25.86

19.19

54.95

0.01

0.01

0.25

Biod.

T-7777

Biod.

Biod.

Biod.

Biod.

32.64

23.93

43.43

0.02

0.02

0.25

Biod.

T-7861

6.01

21.57

47.76

30.67

24.29

25.45

50.27

0.01

0.01

0.23

Biod.

T-7895

Biod.

21.17

33.43

45.40

23.14

28.75

48.11

Biod.

Biod.

Biod.

Biod.

T-7911

Biod.

Biod.

Biod.

Biod.

17.97

17.04

64.99

Biod.

Biod.

Biod.

Biod.

T-7928

Biod.

14.34

36.37

49.29

21.39

35.88

42.72

0.00

0.00

0.27

Biod.

T-8084

10.08

10.02

41.03

48.95

22.84

31.42

45.74

0.06

0.06

0.37

Biod.

T-8145

21.61

29.71

60.68

9.61

39.37

21.73

38.91

0.08

0.07

0.48

Biod.

T-8211

Biod.

12.68

37.20

50.12

22.79

29.37

47.84

0.00

0.00

0.26

Biod.

T-8233

Biod.

Biod.

Biod.

Biod.

20.85

27.28

51.87

0.00

0.00

0.26

Biod.

T-8243

Biod.

9.54

42.73

47.73

16.51

25.38

58.12

0.00

0.00

0.23

Biod.

T-8255.5

Biod.

Biod.

Biod.

Biod.

18.77

22.34

58.88

0.00

0.00

0.29

Biod.

T-8275

Biod.

10.99

48.05

40.96

22.25

28.13

49.62

Biod.

Biod.

Biod.

Biod.

T-8302.5

Biod.

12.19

35.98

51.83

19.43

26.75

53.82

0.01

0.01

0.30

Biod.

T-8312.5

Biod.

15.31

48.60

36.09

21.29

32.77

45.94

0.01

0.01

0.32

Biod.

T-8317

8.38

16.28

31.44

52.28

25.28

15.67

59.05

0.04

0.04

0.41

Biod.

T-8332.5

Biod.

Biod.

Biod.

Biod.

20.21

28.35

51.44

0.01

0.01

0.30

Biod.

T-8338

Biod.

Biod.

Biod.

Biod.

23.53

32.02

44.45

0.01

0.01

0.27

Biod.

T-8354.5

Biod.

Biod.

Biod.

Biod.

19.96

28.73

51.31

0.01

0.01

0.27

Biod.

T-8370.5

Biod.

Biod.

Biod.

Biod.

20.64

27.13

52.24

0.01

0.01

0.28

Biod.

T-8380

Biod.

12.19

35.16

52.65

18.84

27.41

53.75

0.00

0.00

0.26

Biod.

T-8431

Biod.

Biod.

Biod.

Biod.

12.47

17.54

70.00

0.01

0.01

0.30

Biod.

T-8448

Biod.

Biod.

Biod.

Biod.

19.87

24.55

55.58

0.01

0.01

0.33

Biod.

T-8850

15.25

23.00

50.80

26.20

19.47

22.46

58.07

0.02

0.02

0.21

0.17

T-8870

12.05

20.60

46.16

33.24

21.50

24.58

53.92

0.05

0.05

0.29

0.28

T-8890

13.21

25.90

43.51

30.59

13.13

51.35

35.52

0.50

0.33

0.23

0.07

T-9150

18.34

29.75

44.92

25.33

32.12

28.03

39.84

0.06

0.06

0.28

0.54

T-9790

17.55

47.46

34.61

17.93

32.75

29.28

37.97

0.08

0.08

0.28

0.39

T-10079

Biod.

Biod.

Biod.

Biod.

32.69

38.10

29.21

0.05

0.04

0.26

Biod.

T-11610

15.57

45.83

31.19

22.98

13.81

50.48

35.72

0.49

0.33

0.25

0.09

T-11650

11.80

41.88

27.98

30.14

12.77

51.59

35.64

0.52

0.34

0.24

0.05

T-11670

11.33

44.43

28.36

27.21

12.48

50.82

36.69

0.48

0.32

0.24

0.08

T-11690

11.53

44.18

31.22

24.60

21.15

28.86

49.99

0.06

0.05

0.27

0.25

T-11710

14.70

45.19

32.13

22.68

12.73

52.35

34.92

0.53

0.35

0.24

0.07

T-11730

14.18

47.33

32.58

20.09

14.02

50.67

35.31

0.49

0.33

0.24

0.08

T-11790

14.94

45.90

28.74

25.36

16.88

48.17

34.95

0.47

0.32

0.25

0.11

T-11810

17.04

48.93

34.42

16.65

18.37

47.11

34.52

0.43

0.30

0.25

0.10

T-11870

18.89

50.04

31.28

18.68

17.14

48.41

34.44

0.45

0.31

0.24

0.12

TT19/TT23: C19 tricyclic terpane/C23 tricyclic terpane; TT21/TT23: C21 Tricyclic terpane/C23 tricyclic terpane; TT23/H30: C23 tricyclic terpane/C30αβ-Hopane; TT24/H30: C24 tricyclic terpane/C30αβ-Hopane; TTe24/H30: C24 tetracyclic terrpane/C30αβ-Hopane; TT25/TT26: C25 tricyclic terpane/C26 tricyclic terpane; Ts/(Ts + Tm): 18α(H)-22,29,30-trisnorhopane/18α(H)-22,29,30-trisnorneohopane + 17α(H)-22,29,30-trisnorhopane; 29Ts/H30: C29 trisnorhopane/C30αβ-hopane; M30/H30: C30 moretane/C30αβ-Hopane; O.I.: Oleanano Index (Oleanane/C30αβ-Hopane) × 100; G.I.: Gammacerane Index (Gamacerane/C30αβ-Hopane) × 100; HH32 I.I.: C32 Isomerization Index; HH32 H.I.: C32 Homohopane Index; HH35/HH34: C35 Homohopane/C34 Homohopane; TT/PT: ∑ Tricyclic Terpane/∑ Pentacyclic Terpane; BNH I.: Bisnorhopane Index (25-Norhopano/C30αβ-Hopane) × 100

Geochemical correlations based on the tricyclic terpanes such as TT19/TT23, TT23/TT30, TT24/TT30 and TT25/TT26 are excellent indicators of source and depositional environment. Thus, Table 3 shows that TT19/TT23 ratios vary between 0.06 and 0.58, except for the sample T-1190 that presents a value of 1.10. These low ratios suggest an important bacterial/algal over terrestrial origin. TT21/TT23 ratios present values > 1.0 for most of the samples corroborating a marine origin associated with prokaryotic organisms (algal/bacterial). However, in the shallower intervals of the Cascajal and Tangareal del Mira Fm, the TT21/TT23 ratios display values slightly higher than 1, indicating a combined contribution of bacterial/algal O.M. with a significant terrestrial input.

TT23/30H ratios and Σtricyclic terpanes/Σhopanes do not show a trend that clearly shows the origin of the O.M. along the stratigraphic column. Values vary alternately around 1.0, indicating a significant higher plant (continental) contribution to the O.M. toward the shallower formation of Cascajal and Tangareal del Mira, while in the deepest part of the well, the Tumaco Fm, the O.M. is mainly marine contributions from bacterial/algal inputs. C24TeT/C30-hopane ratios are quite used in the characterization of the paleodepositional environment (Peter et al. 2005). The highest abundances of tetracyclic terpane C24TeT have been found in marine-deltaic and lacustrine saline environments (Rocha-Mello et al. 1988). In Tumaco-1-ST-P, C24Te/H30 ratios present values < 0.44, which dismisses a carbonate or evaporitic environment but it supports a marine shale or marine-deltaic depositional environment. Burwood et al. (1990) found that marine bitumen and crude oils from West Africa showed TT25/TT26 ratios > 1.0, while terrestrial bitumen showed TT25/TT26 values < 1.0. Thus, in the Tumaco-1-ST-P well, this ratio confirms the marine origin of the studied samples as is shown in Fig. 13. Since TT24/TT23 is greater than 0.5 for most of the samples in Tumaco-1-ST-P suggest organic facies associated with marine shales.
Fig. 13

Geochemical correlation between 26/25 tricyclic terpanes versus 24/23 tricyclic terpanes in the organic extracts from rock in Tumaco-1-ST-P, Tumaco basin, Colombia

Steranes in selected samples from Tumaco-1-ST-P (Fig. 12) allow observing that pregnanes, excellent indicators of salinity, are present in medium concentration, although in some samples these are biodegraded or have not been formed. The C27 diasteranes (rearranged steranes) are present in significant concentrations, which suggest a silisiclastic environment (27D/29ααR > 1.0). C27-, C28-, and C29-steranes are present in varying concentrations and without any predominance between them, which suggest alternating contributions of algal/microbial and land plants (transitional environment) origin. The configuration of ααR-sterane in most of the samples is greater than ββ-R-S or ββ-S, which indicates an immature O.M.

The diasteranes/steranes ratio is routinely used in geochemical studies to distinguish between carbonate and siliciclastic source rocks. Low values of this ratio in bituminous extracts indicate anoxic carbonate source rocks poor in clays. On the contrary, high diasteranes/esteranes ratios are typical of bitumen derived from source rocks containing abundant clays (Cortes et al. 2018). The diasterane/sterane (27-dia/29ααR) ratios for Tumaco-1-ST-P well show values > 2.0, which clearly indicates a higher diasteranes content over the regular steranes, suggesting that this organic matter was deposited on siliciclastic rocks in a transitional marine-continental environment.

The 20S/(20S + 20R) ratio is one of the maturity parameters more frequently used in petroleum geochemistry. The isomerization of carbon C20 on the C29-5α(H),14α(H),17α(H)-sterane causes an increase in the 20S/(20S 20R) ratio between 0.0 to ≈ 0.5 with an increment of the maturity (equilibrium between 0.52 and 0.55, Seifert and Moldowan 1986) (Cortes et al. 2018). Bitumen in Tumaco-1-ST-P well has values in the range between 0.0 and 0.4 (average 0.13), which indicates a very low maturity. The C29 ββ/(ββ + αα) ratio typically presents its thermal equilibrium between 0.68 and 0.72. Bitumen extracts from Tumaco-1-ST-P rocks show a value around 0.1, confirming that these samples are immature or in the diagenetic stage.

Maturity evolution

Aromatic hydrocarbons

Thermal maturity is the most important process in evaluation of oil and gas potential. Geochemical correlations based on aromatic hydrocarbons can be potentially better than those obtained in the saturated biomarkers fraction due to they are sensitive to differences in thermal maturity from the middle stage to the final part of the window of hydrocarbons generation (Radke 1988). A great variety of geochemical ratios based on the composition of the aromatic fraction has been proposed associated with the relationship between the concentration of the more thermally stable isomers and their counterparts less stable (Radke and Welte 1983; van Aarssen and de Leeuw 1999).

Maturity parameters derived from methylnaphthalenes (MN) are based on the idea that naphthalenes with compound methyl β-substituted are more stable than those with methyl α-substituted. The maturity parameters based on the phenanthrene (P) and methylphenanthrenes (MP) are based on the high stability of the 3-MP and 2-MP compared with 9-MP and 1-MP (Radke and Welte 1983). The isomers of the alkyldibenzothiophenes (MDBT) with a methyl substituent in position 4 are more thermodynamically stable, whereas isomers with a methyl substituent in position 1, have low stability (Chakhmakhchev et al. 1997).

In Tumaco-1-ST-P bitumen extracts, the aromatic hydrocarbons were identified based on full-scan GC/MS analysis and quantified by GC/MS-SIM mode using the selected ions for alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, mono- and triaromatic steroids (Sect. 3.6) comparing the mass fragmentograms with data previously reported (Hughes 1984; Budzinski et al. 1995; van Aarssen and de Leeuw 1999) and with bitumen and crude oils of known composition (e.g., NGS NSO-1 oil sample, NPD-Nigoga) (NPD-Nigoga 2000).

Figure 14 shows the alkylnaphthalenes, alkylphenanthrenes, and alkyldibenzothiophenes fragmentograms for sample T-11610 of Tumaco-1-ST-P well, while Table 4 displays the main geochemical correlation with aromatic results. There is evidence that in the hydrocarbon generation window, the aromatic hydrocarbons show systematic changes with an increment in the thermal maturity (Hughes 1984; Radke and Welte 1983; Alexander et al. 1985). However, in an early stage (diagenesis), the geochemical parameters based on the alkylaromatics, as in Tumaco-1-ST-P, show an irregular behavior due to quick variations in the organic facies, control from source effects, thermal stress, and biodegradation of the O.M.
Fig. 14

Alkylnaphthalenes, alkylphenanthrenes, dibenzothiophene and alkyldibenzothiophenes de la muestra T-11610, Tumaco-1-ST-P, Tumaco basin, Colombia (see foot Table 4 for compound identification)

Table 4

Geochemical ratios based on Aromatic Hydrocarbons in organic extracts from rocks and cuttings in Tumaco-1-ST-P, Tumaco basin, Colombia

Sample

Alkylnaphathalenes

Alkylphenanthrenes

Alkylbenzothiophenes

Monoaromatic and triaromatic steroids

MNR

DNR

TMNR

MPR

MPI-1

DBR

MDBTR

DBT/P

TAS/(MAS + TAS)

26S/28S (TAS)

27R/28R (TAS)

T-1130

1.75

2.15

0.97

0.92

0.61

3.20

2.29

0.23

0.90

0.61

0.99

T-1190

2.33

2.40

0.20

2.30

1.14

3.70

3.29

0.14

0.17

0.35

0.59

T-1290

2.45

2.72

0.12

2.43

1.32

3.09

4.46

0.24

0.53

0.46

0.70

T-2490

2.26

3.57

0.34

1.99

0.67

3.70

2.99

0.14

0.46

0.45

0.81

T-2550

1.09

3.17

0.28

2.16

0.84

4.38

4.34

0.16

0.36

0.34

0.49

T-2570

1.61

5.67

0.41

1.96

0.85

5.05

3.76

0.14

0.34

0.39

0.46

T-2590

1.50

3.23

0.30

2.35

0.92

3.95

3.81

0.11

0.43

0.38

0.42

T-2610

1.52

2.06

0.24

1.81

0.68

2.79

3.29

0.12

0.10

0.96

1.15

T-4130

1.37

2.21

0.41

1.95

0.49

3.13

2.14

0.28

0.30

1.21

0.57

T-4330

0.70

1.92

0.36

1.64

0.63

3.65

1.83

0.23

0.34

1.27

0.32

T-4410

0.96

3.44

0.45

1.79

0.60

3.97

2.06

0.30

0.39

1.18

0.36

T-4470

0.66

1.11

0.40

1.53

0.64

1.96

1.45

0.28

0.40

1.47

0.49

T-5030

1.47

1.49

0.37

1.86

0.71

2.47

3.49

0.11

0.64

0.49

0.83

T-5394

2.18

9.91

0.33

1.79

0.91

5.02

2.28

0.10

0.09

0.79

0.18

T-5475

1.85

2.96

0.36

1.60

0.47

2.67

2.64

0.15

0.15

1.30

1.18

T-5509

1.07

5.48

0.47

1.43

0.44

3.36

4.75

0.18

0.34

3.41

0.09

T-5560

1.94

4.94

0.32

0.94

0.50

3.56

5.40

0.14

0.18

3.01

0.08

T-5570

1.13

4.63

0.52

1.84

0.87

4.19

3.60

0.13

0.14

0.76

0.65

T-5650

1.41

1.87

0.22

2.15

1.00

2.54

3.25

0.17

0.22

0.92

1.16

T-5750

5.19

21.47

0.21

1.93

1.21

4.06

4.80

0.17

0.10

1.00

1.54

T-5810

1.72

1.66

0.41

2.05

0.86

2.81

3.46

0.13

0.11

1.12

1.44

T-5890

2.01

1.18

0.37

1.94

0.67

2.41

3.36

0.12

0.12

0.99

1.64

T-5910

2.25

0.99

0.26

1.92

0.77

1.82

3.31

0.18

0.16

0.91

1.83

T-5950

2.01

1.27

0.38

2.00

0.41

2.53

3.47

0.10

0.13

1.20

1.97

T-5990

2.69

1.85

0.24

1.70

0.50

2.97

3.06

0.10

0.16

1.30

1.80

T-6010

2.40

0.86

0.20

1.84

0.50

1.59

3.11

0.10

0.18

1.02

2.01

T-6070

1.58

1.96

0.42

1.71

0.38

3.29

3.37

0.08

0.12

1.19

1.90

T-6090

2.06

2.02

0.25

1.63

0.60

3.12

2.01

0.10

0.11

1.54

6.10

T-6110

1.89

1.31

0.23

1.67

0.58

2.39

3.78

0.15

0.15

0.94

1.89

T-6130

1.27

1.36

0.22

2.36

0.49

2.21

3.68

0.11

0.14

1.02

1.85

T-6150

1.44

0.74

0.20

1.72

0.64

1.50

3.36

0.12

0.12

1.16

1.96

T-6170

1.78

1.90

0.38

1.73

0.58

3.63

3.00

0.13

0.13

0.97

2.01

T-6190

2.97

1.38

0.22

1.90

0.69

2.77

3.03

0.11

0.13

1.19

1.93

T-6210

1.01

2.59

0.38

2.16

0.69

3.76

3.56

0.13

0.24

0.60

0.63

T-6250

1.92

1.36

0.34

1.97

0.65

2.22

3.80

0.14

0.17

0.98

1.82

T-6310

2.19

1.25

0.31

2.13

0.47

2.40

4.39

0.10

0.28

0.75

1.64

T-6390

1.76

0.79

0.23

2.29

0.72

1.52

4.17

0.08

0.15

0.82

1.74

T-6430

2.22

2.20

0.21

1.95

0.90

2.91

3.75

0.11

0.19

0.99

1.77

T-6550

2.18

1.24

0.29

2.02

0.74

2.26

3.35

0.10

0.16

1.00

1.97

T-6570

2.37

1.42

0.21

2.13

0.78

2.40

3.60

0.10

0.16

1.11

2.02

T-6590

1.82

0.94

0.22

1.96

0.72

1.82

3.65

0.11

0.18

0.88

1.82

T-6630

1.17

0.72

0.20

2.00

0.67

1.58

3.70

0.10

0.14

0.89

1.83

T-6710

0.82

2.82

0.46

2.02

0.64

4.23

3.26

0.14

0.07

1.16

2.41

T-6750

1.50

1.84

0.41

1.93

0.71

3.12

3.47

0.12

0.09

0.94

1.97

T-6770

2.00

1.21

0.36

1.88

0.67

2.42

3.15

0.12

0.08

0.92

2.98

T-6790

0.96

1.79

0.41

1.93

0.66

3.19

3.14

0.11

0.11

1.17

2.49

T-6810

0.88

2.03

0.42

1.88

0.65

3.41

3.14

0.11

0.07

1.20

2.66

T-6830

1.77

1.17

0.25

1.84

0.65

2.14

2.95

0.10

0.07

1.36

2.46

T-6850

1.39

2.13

0.44

1.92

0.69

3.16

3.34

0.11

0.06

0.81

1.32

T-6890

1.95

1.11

0.31

1.90

0.70

2.04

3.08

0.11

0.09

0.92

1.89

T-7050

0.84

1.06

0.31

2.17

0.75

2.68

3.30

0.10

0.12

1.02

1.98

T-7110

2.37

1.00

0.18

1.95

0.72

2.32

3.31

0.11

0.09

0.88

1.80

T-7130

2.47

1.53

0.19

1.70

0.67

3.07

3.15

0.18

0.08

0.88

1.97

T-7210

2.74

2.82

0.10

1.55

0.56

4.68

2.90

0.13

0.08

0.96

2.20

T-7230

0.89

2.75

0.10

1.57

0.64

5.23

2.84

0.15

0.16

1.02

2.19

T-7290

1.99

1.07

0.25

1.71

0.51

2.40

2.71

0.15

0.07

1.06

2.31

T-7310

1.74

1.06

0.43

2.30

0.68

2.03

2.99

0.12

0.11

0.93

2.29

T-7330

1.91

1.16

0.30

2.06

0.45

2.29

3.29

0.16

0.16

0.91

2.10

T-7450

1.94

4.35

0.17

1.88

1.05

4.87

2.58

0.09

0.12

0.84

1.39

T-7470

1.47

1.14

0.20

1.83

0.74

2.56

3.14

0.11

0.13

0.93

1.86

T-7591

1.33

3.98

0.14

1.31

0.71

7.24

1.56

0.22

0.06

0.45

2.37

T-7693

2.17

1.35

0.52

1.42

0.61

2.05

1.83

0.24

0.20

0.47

0.61

T-7712

2.04

3.69

0.41

1.15

0.49

3.02

2.45

0.18

0.10

0.71

1.50

T-7777

2.51

10.20

0.26

1.30

0.58

5.70

1.64

0.14

0.08

0.94

3.36

T-7861

1.30

3.51

0.51

0.99

0.52

3.67

1.98

0.25

0.10

0.36

3.13

T-7895

0.41

0.82

0.63

1.65

0.16

1.47

6.75

0.01

0.26

0.48

0.83

T-7911

1.87

0.49

0.59

1.62

0.19

1.18

9.05

0.01

0.30

0.21

0.59

T-7928

1.48

0.73

0.60

1.50

0.21

1.40

9.92

0.01

0.24

0.52

1.49

T-8084

1.82

2.11

0.40

1.29

0.32

2.00

5.29

0.02

0.18

0.34

0.52

T-8145

2.08

5.63

0.25

1.36

0.43

4.30

4.09

0.03

0.10

0.45

0.47

T-8211

1.79

0.34

0.56

2.45

0.14

0.87

4.06

0.01

0.14

1.76

0.67

T-8233

3.04

1.02

0.34

2.32

0.15

1.61

8.62

0.01

0.30

0.76

0.52

T-8243

1.09

0.24

0.64

2.11

0.19

0.97

11.18

0.01

0.34

0.41

0.98

T-8255.5

2.18

1.03

0.44

1.87

0.36

1.67

4.75

0.12

0.15

0.61

2.22

T-8275

0.47

0.22

0.75

1.55

0.29

1.05

5.97

0.12

0.27

0.28

1.07

T-8302.5

0.25

0.30

0.68

2.10

0.16

0.94

15.26

0.01

0.34

1.60

0.43

T-8312.5

1.63

0.13

0.59

1.96

0.17

0.78

17.92

0.01

0.38

0.75

1.84

T-8317

2.05

0.13

0.41

2.16

0.18

0.90

16.53

0.01

0.38

0.34

0.50

T-8332.5

1.96

0.72

0.37

1.80

0.15

1.44

10.82

0.01

0.53

0.55

1.63

T-8338

2.01

0.37

0.51

3.57

0.29

0.96

14.70

0.02

0.39

0.45

1.19

T-8354.5

0.28

0.19

0.66

2.17

0.16

1.02

15.36

0.01

0.35

0.37

1.15

T-8370.5

0.29

0.32

0.67

1.72

0.16

1.18

11.54

0.01

0.47

0.38

0.56

T-8380

1.93

0.90

0.15

2.11

0.70

1.74

2.95

0.17

0.22

0.50

0.68

T-8431

0.38

0.43

0.68

1.55

0.16

1.24

10.02

0.01

0.59

0.28

0.63

T-8448

0.49

0.28

0.65

1.68

0.15

1.05

9.57

0.01

0.49

0.33

0.56

T-8850

2.24

0.78

0.23

1.92

0.25

1.69

8.16

0.03

0.35

0.56

0.77

T-8870

2.06

0.15

0.41

1.72

0.23

0.74

10.98

0.02

0.47

0.57

0.63

T-8890

1.25

3.20

0.45

3.12

1.04

3.71

11.01

0.09

0.31

0.22

1.47

T-9150

3.54

1.67

0.15

2.05

0.66

2.81

3.66

0.16

0.11

0.68

1.87

T-9790

1.90

0.86

0.27

1.84

0.66

1.85

3.75

0.08

0.15

0.61

1.39

T-10079

0.99

0.29

0.63

1.38

0.16

0.98

14.10

0.01

0.07

0.20

0.30

T-11610

1.80

6.22

0.44

2.79

1.00

4.66

8.76

0.15

0.17

0.27

1.35

T-11650

1.13

4.67

0.49

1.96

0.84

4.05

11.25

0.11

0.25

0.18

1.35

T-11670

1.53

3.36

0.44

2.91

1.08

3.72

14.06

0.09

0.23

0.25

1.36

T-11690

1.90

0.62

0.22

1.96

0.28

1.55

9.90

0.02

0.32

0.46

1.12

T-11710

1.13

3.85

0.51

3.04

1.09

3.71

8.24

0.10

0.36

0.19

1.31

T-11730

1.46

4.92

0.51

2.88

1.02

4.66

11.13

0.09

0.26

0.22

1.47

T-11790

1.45

2.24

0.38

2.70

1.03

3.18

8.16

0.10

0.19

0.29

1.62

T-11810

1.21

2.59

0.43

2.49

0.13

3.53

7.47

0.01

0.13

0.34

1.60

T-11870

1.10

3.05

0.44

3.05

1.07

3.64

8.42

0.10

0.22

0.28

1.61

MNR = [2MN]/[1MN], Methylnaphthalene ratio; DNR = [2,6-DMN] + [2,7-DMN]/[1,5-DMN], Dimethylnaphthalene ratio; MPR = [2-MP]/[1-MP], Methylphenanthrene ratio; MPI-1 = 1.5[2-MP] + [3-MP]/[P] + [1-MP] + [9-MP], Methylphenanthrene Index-1; MPI-2 = 3[2-MP]/[P] + [1-MP] + [9-MP], Methylphenanthrene Index-2; DBTR-1 = [2- + 3-MDBT]/[1-MDBT], Dibenzothiophene ratio-1; DBTR-2 = [4-MDBT]/[DBT], Dibenzothiophene Ratio-2; DBTR-4 = [1-MDBT]/[DBT], Dibenzothiophene ratio-4; MDBTR = [4-MDBT]/[1-MDBT], Methyldibenzothiophene ratio; MDBTR-1 = [2,4-DMDBT]/[1,4-DMDBT], Dimethyldibenzothiophene ratio-1; MDBTR-2 = [4,6-DMDBT]/[1,4-DMDBT], Dimethyldibenzothiophene ratio-2; Ro = Vitrinite Reflectance; – = data not available

Methylnaphthalenes are found and widely distributed in the sedimentary organic matter (Tissot and Welte 1984). Their distribution is highly variable among samples (even in the same producer field or in a stratigraphic column) (van Aarssen and de Leeuw 1999). The sesquiterpanes and triterpenoids derived from microorganisms and superior plants appear to be the origin of the MN (Püttman and Villar 1987), where they are produced through isomerization and transmethylation reaction in an environmental rich in acid clays. In Tumaco-1-ST-P, MN ratios vary between 0.25 and 5.19 (mean 1.68±0.73) indicating a high variability in the maturity and suggesting a common origin but different states of thermal maturity consistent with an intense diagenetic biodegradation process. As the thermal maturity increases, the predominance of 2-MN over 1-MN increases. This increment toward the depth must be interpreted as an increase in the maturity toward deeper intervals (Tumaco Fm, late Oligocene). The dimethylnaphthalenes ratios (DNR) vary between 0.03 and 21.5 indicating a wide maturity distribution. Among TMNs, the most abundant isomer for a mixture in equilibrium (highly mature) is the 2,3,6-TMN, and one of the less abundant is the 1,2,5-TMN, which is often the most abundant in immature samples (Budzinski et al. 1995). van Aarssen and de Leeuw (1999) found that the presence of 2,3,6-TMN is very low in the diagenetic stage and increases dramatically in samples highly mature in which this isomer is dominant over the 1,3,7-TMN and 1,3,6-TMN.

The distribution of alkylphenanthrenes can be used as an indicator of source, in addition to its well known use as a parameter of maturity (Armstroff et al. 2006). Differences due to variations in the thermal maturity are in many cases gradual, while changes in the source of the O.M. are characterized by drastic differences. The alkylphenanthrenes distribution is dominated by 2-MP and 9-MP isomers at any stage of maturity. In Tumaco-1-ST-P well, 2-MP and 9-MP are predominant over 1-MP and 3-MP indicating a marine origin (Budzinski et al. 1995).

Methylphenanthrene-1 and -2 indices (MP-1 and MP-2) proposed by Radke and Welte (1983) are perhaps the most widely used indices to determine the maturity based on aromatic hydrocarbons. The utility of this geochemical parameter rests on the relative stability of the various methylphenanthrene isomers. Due to its linear relationship with the vitrinitic reflectance within the generation window, MPI-1 is often used to infer the value of the equivalent vitrinitic reflectance (Rc,  %) in crude oils (Radke 1988) and could be used in source rocks and bituminous extracts of outcrops where the vitrinitic reflectance cannot be measured. The MPI-1 values in Tumaco-1-ST-P show an average value of 0.60 and a mean value of Rc of 0.76%.

Since 4-methyldibenzothiophene isomer is more stable than 1-methyldibenzothiophene, the 4-/1-methyldibenzothiophene (MDBTR) was proposed as an indicator of maturity (Radke et al. 1986). This ratio is quite sensitive to the maturity, correlating well with the vitrinitic reflectance and with Tmax parameter from pyrolysis Rock–Eval in rock samples (Radke 1988). Dzou and Hughes (1993) noted that MDBTR is particularly robust to assess maturity in samples with high thermal maturity (condensates, lighter crudes). The organic extracts of the Tumaco-1-ST-P well presented an average value of 5.40, indicating that the 4-methyldibenzothiophene is in the highest concentration that 1-methyldibenzothiophene. The maturity based on MDBT ratios increases from surface to bottom in the column reaching the highest values in the Tumaco Fm between the early and middle Miocene.

The dibenzothiophene/phenanthrene ratio (DBT/P) is thought to be an indicator of source rock lithology (Radke et al. 1986, Hughes et al. 1995) with carbonates having ratios > 1 and shales < 1. When this ratio is plotted against Pr/Ph, the depositional paleoenvironment may be inferred regarding microbiological and chemical processes (Hughes et al. 1995). Figure 15 shows a plot of DBT/P versus Pr/Ph associated with rock lithology for a bituminous extract of Tumaco-1-ST-P, indicating that samples fall in the area of a lacustrine and marine shale environment (zones 2 and 3, respectively). The zone 2 suggests a variable lithology of the rock with values of DBT/P < 1 and values of Pr/Ph < 1 and characterizing an lacustrine environment, while the zone 3 presents a lithology of shale, in an marine environment and DBT/P < 1 and Pr/Ph in the range between 1 and 3.
Fig. 15

Geochemical correlation between DBT/P versus Pr/Ph in the organic extracts from rock in Tumaco-1-ST-P, Tumaco basin, Colombia

Molecular stratigraphy in Tumaco-1-ST-P

The molecular stratigraphic interpretation allows to conclude that organic facies and lithology in Tumaco-1-ST-P are characterized in Cascajal and Tangareal del Mira Fms. (1000–5000 ft) by a marine-deltaic paleoenvironment with an important terrestrial contribution and varying between deltaic plain and prodelta during the late Miocene as is supported by C15+ n-alkanes profiles, CPI, Pr/Ph, TAR, oleanane index, and tricyclic/pentacyclic terpanes (Internal communication stratigraphy Antek S.A.-Paleoxplorer in ANH-Antek S.A. 2013). At the top of Tumaco Fm (5000–9000 ft) in the late to medium Miocene, the depositional environment was like to the marine delta of the Tangareal del Mira Fm, changing to a marine platform environment at 8000 to 10,000 ft depth in the middle to early Miocene, which is confirmed by high ∑tricyclic terpanes/∑pentacyclic terpanes, low oleanane index, high C35/C34 homohopanes ratios. Toward the bottom of the column (10,000–12,000 ft), Tumaco Fm was deposited in the late Oligocene under a marine shelf environment, which is supported by Pr/Ph < 1.0, DBT/P < 1.0, low C26/C25 tricyclic terpanes ratios, high C24/C23 tricyclic terpanes ratios.

Conclusions

Total organic carbon in samples from Tumaco-1-ST-P presented an average value of 0.95% on a population of 250 samples analyzed, with a variation between 0.09 and 2.30%. This variability suggests a temporal and spatial variations of organofacies in the sedimentary record. Results of Rock–Eval pyrolysis showed that S1 peak varies between 0.02 and 0.80 mg HC/g rock, which classifies the O.M. with a “poor to acceptable” generation potential. S2 peak varied between 0.07 and 10.45 mg HC/g rock (average 1098±1.36 mg HC/g rock). Peak S3 showed values between 0.20 and 7.60 mg CO2/g rock, while Tmax values varied in the range between 328 and 445 °C, which indicates a relative immaturity of the O.M. (diagenetic maturity).

Geochemical correlations based on screening data allowed to conclude that S2/S3 varied in the range between 0 and 10, whereas HIpd presented three major peaks that classified the O.M. quality with a type III and/or type II/III kerogen. This classification would expect that the main product generated will be crude oil and/or crude oil/gas, special in the deepest intervals of the well. Production index varied between 0.02 and 0.36 classifying these rocks in a immature generation stage. However, the combination of the I.P with other maturity parameters allowing to look, in a more discreet way, that the column covers a wide range of maturity from a kerogen oil–gas-prone type II/III to a kerogen non-generator type IV, indicating that the O.M. in the study does not come from a single and unique kerogen due to the large variation in paleodeposicional environments. On the basis of the modified van Krevelen diagram, the type III kerogen, which is responsible for the majority of immature samples from Tumaco-1-ST-P well was characterized to have low H.I (50–200 mg HC/g TOC), low H/C atomic ratios (0.7–1.0), and high O/C values (> 0.3).

Vitrinite reflectance (Ro) varied between 0.1978 and 0.5418% (mean 0.4046±0.056%), suggesting an immature O.M. The maceral groups found were vitrinite, liptinite, and inertinite, which allowed us to identify the following types of macerals: esporinite, cutinite, resinite, alginite, colotelinite, colodetrinite, funginite, exsudinite, exsudatinite, inertodetrinite, among others. The EOM,  % oscillation between 0.0018% and 0.75%, being the highest contents toward the late Oligocene in the Tumaco Fm.

SARA fractionation presented high values for the resin fraction in most of the organic extracts, varying between 17.47 and 62.33%. The asphaltenes varied in a range between 4.65 and 59.02%, the aromatic fraction ranging between 0 and 21.28% is the fraction of which were obtained lower recoveries. Finally, saturated fraction ranged between 4.99 and 43.81%. The Tissot and Welte’s ternary diagram indicates that the organic matter extracted was of naphthenic characteristics.

C15+ GC/FID analysis of the saturated fraction showed a bimodal distribution in hydrocarbons resolved between n-C15 and n-C32, although some chromatograms extend their distribution to n-C36, with a maximum around n-C19 to n-C20 suggesting an algal/bacterial input, while the second peak occurs around n-C29 to n-C31, indicating a continental contribution (terrestrial), allowing to conclude that this is a mixed O.M. originated from type II/III kerogen. The geochemical correlations based on C15+ saturated fraction show a CPI characteristic of a low maturity and marine/continental origin. Pr/Ph ratio suggests a bitumen derived from marine shale, additionally Pr/Ph < 3.0, indicating that O.M. was deposited in suboxic to oxic conditions. Pr/n-C17 varied between 0.53 and 5.74, while Ph/n-C18 ranges between 0.22 and 4.88, indicating low maturity. TAR values suggested that O.M. has an important aquatic algal/bacterial input over terrestrial contributions.

Geochemical correlations based on saturated fraction biomarkers analyzed by GCMS showed that TT21/TT23 present values > 1.0 for most of the samples corroborating the marine origin associated with prokaryotic organisms (algal/bacterial). However, in the deepest intervals (late Oligocene of Tumaco Fm), TT21/TT23 present values slightly higher than 1.0, indicating a combined and alternated contribution of bacterial/algal with less terrestrial contribution. C24Te/H30 ratios showed values < 0.44, which dismisses a carbonate or evaporitic environment but supports a marine shale or marine-deltaic depositional environment. TT25/TT26 ratios in all samples, without exceptions, showed values > 1, which confirms a marine origin.

Tm ≤ Ts suggests a diagenetic maturity. Ts/(Ts + Tm) ratios presented values < 0.7, with a high amount of results ranging between 0.02 and 0.5 suggesting a low maturity. When this parameter is used as an depositional environment indicator, the average value of 0.40 found in the Tumaco-1-ST-P well indicates a marine-deltaic environment. The oleanane index > 20% corroborates a terrestrial O.M. input with marine contribution and the Miocene–Pliocene as the age of this organic matter. Many samples in the Tumaco-1-ST-P well showed a high concentration of gammacerane and low Pr/Ph ratios indicating a high salinity and saline stratification of the water column during deposition.

The ββ-steranes values decreased as  %C27αββ > %C28αββ > %C29αββ, corroborating a marine environment with minor terrestrial contributions. C27 αα-R, C28 αα-R and C29 αα-R (biosteranes) are present in high concentrations confirming a thermal immaturity of these samples. C29 ααα-(S/R) ratios present values < 1.0, which indicates that the αα-R-sterane configurations are in higher concentrations over the αα-S configuration (geosteranes, more stable thermodynamically) and consequently highly immature. Diasteranes/steranes (27-DIA/29 αα-R) ratios in Tumaco-1-ST-P well presented values > 2.0, indicating that this organic matter was deposited on silisiclastic rocks in a transitional marine-terrestrial environment. 20S/(20S + 20R) ratios are in the range between 0.0 and 0.4 (average 0.13), which indicates a very low maturity, while the C29ββ/(ββ + αα) ratios with a value around 0.1 indicate that the O.M. studied is below the equilibrium range (below hydrocarbons generation window).

The geochemical correlations based on aromatic hydrocarbons showed that methylnaphthalene ratios (MNR) and trimethylnaphthalene ratios (TMNR) presented a high variability in the samples maturity suggesting a common origin but different stages of thermal maturity consistent with an intense diagenetic biodegradation in progress. The monoaromatic steroids (MAS) decreased in concentration with depth (Pliocene to Oligocene) suggesting a light increment in the thermal maturity. On the other hand, the concentration of triaromatic steroids (TAS) increased proportionally with depth as a result of the MAS transformation into its respective TAS counterpart. This maturity model, although in the diagenetic stage, is consistent with a maturation process in progress in the Tumaco basin, where the Oligocene (Tumaco Fm) showed the greater maturity.

Notes

Acknowledgements

The present discussion about geological setting and regional high-resolution molecular stratigraphy was taken from the technical report presented by Antek S.A. to the ANH-Colombia under contract no. 153-2012. The authors wish to acknowledge National Hydrocarbons Agency, NHA-Colombia for permitting to use the data for the present publication. Paleoexplorer S.A.S. is gratefully acknowledged for the stratigraphy work under sub-contract with Antek S.A.S. RA Geologia is gratefully acknowledged for discussions of the petroleum geology of the study area. JEC and CAV thank to Department of Geosciences, Universidad Nacional de Colombia for supporting this research. The original paper has been beneficiated greatly from the advice and review of an anonymous reviewer.

References

  1. Alexander R, Kagi RI, Roland SJ, Sheppard PN, Chirila TV (1985) The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleum. Geochim Cosmochim Acta 49:385–395CrossRefGoogle Scholar
  2. ANH-Antek S.A. (2013) Estudio integrado de los núcleos del Pozo Tumaco-1-ST-P. Contrato 153-2012. Bogota, ColombiaGoogle Scholar
  3. ANH-Universidad de Caldas (2011) Estudio geológico integrado en la cuenca Tumaco Onshore. Síntesis cartográfica, sísmica, análisis bioestratigráfico, petrográfico, geocronológico, termocronológico y geoquímico de testigos de perforación y muestras de superficie. Contrato 091-2010. Bogota, ColombiaGoogle Scholar
  4. Antek S.A. (2011) Crude oil sampling. Quality manual: analytical procedures manual. Geoquímica & Petróleos Division, Antek S.A. Internal DocumentGoogle Scholar
  5. Armstroff A, Wilkes H, Schwarzbauer J, Littke R, Horsfield B (2006) Aromatic hydrocarbon biomarkers in terrestrial organic matter of Devonian to Permian age. Palaeogeogr Palaeoclimatol Palaeoecol 240:253–274CrossRefGoogle Scholar
  6. Bacon CN, Calver CR, Boreham CJ, Lenman DE, Morrison KC, Revill AT, Volkman JK (2000) The petroleum potential of onshore Tasmania: a review. Geol Surv Bull 71:1–93Google Scholar
  7. Barrero C, Pardo A, Vargas CA, Martinez JF (2007) Colombian sedimentary basins: nomenclature, bondaries, and petroleum geology, a new proposal. Bogota-Colombia. ISBN: 978-958-98237-0-5Google Scholar
  8. Bordenave ML (1993) Applied petroleum geochemistry. Editions Technip, ParisGoogle Scholar
  9. Borrero C, Pardo A, Jaramillo CM, Osorio JA, Cardona A, Flores A, Echeverri S, Rosero S, Garcia Y, Castillo H (2015) Tectonostratigraphy of the Cenozoic Tumaco forearc Basin (Colombian Pacific) and its relationship with the northn Andes orogenic build up. J South Am Earth Sci 39:57–92Google Scholar
  10. Bourbonniere RA, Meyers PA (1996) Sedimentary geolipid records of historical changes in the watersheds and productivities of Lakes Ontario and Erie. Limnol Oceanogr 41:352–359CrossRefGoogle Scholar
  11. Brassell SC, Eglinton G, Marlowe IT, Pflaumann U, Sarnthein M (1986) Molecular stratigraphy: a new tool for climatic assessment. Nature 320:129–133CrossRefGoogle Scholar
  12. Bray EE, Evans ED (1961) Distribution of n-paraffins as a clue to recognition of source beds. Geochim Cosmochim Acta 22:2–15CrossRefGoogle Scholar
  13. Budzinski H, Garrigues P, Connan J, Devillers J, Domine D, Radke M, Oudin JL (1995) Alkilated phenanthrene distributions as maturity and origin indicators in crude oil and source extract. Geochim Cosmochim Acta 59(10):2043–2056CrossRefGoogle Scholar
  14. Burwood R, Cornet PJ, Jacobs L, Paulet J (1990) Organofacies variation control on hydrocarbon generation: a Lower Congo Coastal Basin (Angola) case history. Org Geochem 16:325–338CrossRefGoogle Scholar
  15. Cediel F, Restrepo I, Marin-Ceron M, Duque-Caro H, Cuartas C, Mora C, Montenegro G, Garcia E, Tivar D, Munoz G (2010) Geology and hydrocarbon potential, Atrato and San Juan Basins, Choco (Panama) arc. Tumaco Basin (pacific Realm), Colombia. Fondo Editorial Universidad EAFIT, Medellin, Colombia. ISBN: 978-958-720-052-2Google Scholar
  16. Chakhmakhchev A, Susuki M, Waseda A, Takayama K (1997) Geochemical characteristic of Tertiary oils derived from siliceous sources in Japan, Russia and USA. Org Geochem 27:523–536CrossRefGoogle Scholar
  17. Cortes JE, Aguilera R, Wilches O, Osorno JF, Cortes SI (2018) Organic geochemical insights from oil seeps, tars, rocks, and mud volcanoes on the petroleum systems of the Sinú-San Jacinto basin, Northwestern, Colombia. J S Am Earth Sci 86:318–341CrossRefGoogle Scholar
  18. Didyk BM, Simoneit BRT, Brassell SC, Eglinton G (1978) Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. Nature 272:216–222CrossRefGoogle Scholar
  19. Dzou LI, Hughes WB (1993) Geochemistry of oils and condensates, K field, offshore Taiwan: a case study in migration fractionation. Org Geochem 20:437–462CrossRefGoogle Scholar
  20. Echeverri S, Borrero C, Moreno M, Pardo A, Castillo H (2011) Propuesta de nomenclatura estratigráfica para la sucesión Neógena expuesta en la bahía de Tumaco (Cuenca Tumaco costa adentro, SW de Colombia) redefinición y formalización. Poster, XIV Congreso Latinoamericano de Geología. Medellín. ColombiaGoogle Scholar
  21. Echeverri S, Cardona A, Pardo A, Monsalve G, Valencia VA, Borrero C, Rosero S, Lopez S (2015) Regional provenance from southwestern Colombia fore-arc and intra-arc basins: implication for Middle to Late Miocene orogeny in the Northern Andes. Terra Nova 27(5):1–8CrossRefGoogle Scholar
  22. Espitalié J, Marquis F, Sage L (1987) Organic geochemistry of the Paris Basin. In: Brooks J, Glennie K (eds) Petroleum geology of Northwest Europe. Graham and Trotman, LondonGoogle Scholar
  23. Farrimond P, Poynter JG, Eglinton G (1990) A molecular stratigraphic study of Peru Margin Sediments, Hole 686B, Leg 112. In: Proceedings of the ocean drilling program, scientific results, vol 112Google Scholar
  24. Hall LS, Boreham CJ, Edwards DS, Palu TJ, Buckler T, Hill AJ, Troup A (2016) Cooper basin source rock geochemistry: regional hydrocarbon prospectivity of the Cooper Basin, part 2. Record 2016/06. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2016.006
  25. Hughes WB (1984) Use of thiophenic organosulfur compounds in characterizing crude oils derived from carbonate versus siliciclastic sources. In: Palacas JG (ed) Petroleum geochemistry and source rock potential of carbonate rocks. American Assotiation of Petroleum Geologists, TulsaGoogle Scholar
  26. Hughes WB, Holba AG, Dzou LI (1995) The ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks. Geochim Cosmochim Acta 59:45–90CrossRefGoogle Scholar
  27. IGAC-Ingeominas (2001) Investigacion Integrada del anden Pacifico Colombiano, Tomo I Geologoa. CD room, pp 1–165Google Scholar
  28. International Committee for Coal Petrology (ICCP) (1963) International handbook of coal petrography, 2nd edn. Centre National de la Recherche Scientifique, Paris. [Part II contains methods of analysis, including a section named “recommendations for the preparation of polished surfaces of lump and particulate samples”]Google Scholar
  29. International Organization for Standardization (ISO) (1985) Methods for the petrographic analysis of bituminous coal and anthracite—part 2: preparation of coal samples. ISO 7404-2:1985, GenevaGoogle Scholar
  30. International Organization for Standardization (ISO) (1994) Methods for the petrographic analysis of bituminous coal and anthracite. Part 5: method of determining microscopically the reflectance of vitrinite. ISO 7404-5:1994, GenevaGoogle Scholar
  31. Jarvie DM (2012) Shale resource systems for oil and gas: part 1—Shale-gas resource systems. In: Breyer JA (ed) Shale reservoirs—giant resources for the 21st century. AAPG Memoir, 97, pp 69–87Google Scholar
  32. Jarvie DM, Claxton BL, Henk F, Breyer JT (2001) Oil and shale gas from the Barnett Shale, Fort Worth Basin, Texas. AAPG Bull 85:A100Google Scholar
  33. Jones PJ (1986) The petroleum geochemistry of the paul valley, Anadarko Basin. Master of sciences thesis, University of Oklahoma, Norman, OKGoogle Scholar
  34. Keely BJ, Sinninghe Damste JS, Betts SE, Yue L, De Leeuw JW, Maxwell JR (1993) A molecular stratigraphic approach to palaeoenvironmental assessment and the recognition of changes in source inputs in marls of the Mulhouse Basin (Alsace, France). Org Geochem 20(8):1165–1186CrossRefGoogle Scholar
  35. Kerr AC, Aspden J, Tarney J, Pilatasig LF (2002) The nature and provenance of accreted oceanic terranes in western Ecuador: geochemical and tectonic constraints. J Geol Soc Lond 159:577–594CrossRefGoogle Scholar
  36. Langford FF, Blanc-Valleron MM (1990) Interpreting Rock-Eval pyrolysis data using graphs of pyrolizable hydrocarbons vs. total organic carbon. AAPG Bull 34:34–45Google Scholar
  37. Meyers PA (1997) Organic geochemical proxies of paleooceanographic, paleolimnlogic, and paleoclimatic processes. Org Geochem 27:213–250CrossRefGoogle Scholar
  38. NPD-Nigoga (2000) The norwegian industry guide to organic geochemical analyses. Norwegian Petroleum DirectorateGoogle Scholar
  39. Pawlewicz MJ (2013) Vitrinite reflectance procedure. USGS method for ro. Energy Resources Surveys Team. www.usgs.org
  40. Pawlewicz MJ, Finn TM (2013) New vitrinite reflectance data for the Wind River Basin, Wyoming: U.S. Geological Survey open-file report 2013–1002, 11 ppGoogle Scholar
  41. Peter KE, Walters CC, Moldowan JM (2005) The biomarker guide, vol I and II. Cambridge University Press, CambridgeGoogle Scholar
  42. Peters KE (1986) Guidelines for evaluating petroleum source rock using programmed pyrolysis. AAPG Bull 70:318–329Google Scholar
  43. Peters KE, Cassa MR (1994) Applied source rock geochemistry. In: Magoon LB, Dow WG (eds) The petroleum system-from source to trap. American Association of Petroleum Geologists, TulsaGoogle Scholar
  44. Philp RP (1985) Fossil fuel biomarkers. Applications and spectra. Elsevier Science Publishing Co, New YorkGoogle Scholar
  45. Püttman W, Villar H (1987) Occurrence and geochemical significance of 1,2,5,6-tetramethylnaphthalene. Geochim Cosmochim Acta 51:3023–3029CrossRefGoogle Scholar
  46. Radke M (1988) Application of aromatic compoundsas maturity indicators in source rocks and crude oils. Mar Petrol Geol 5:224–236CrossRefGoogle Scholar
  47. Radke M, Welte DH (1983) The methylphenantrene index (MPI). A maturity parameter based on aromatic hydrocarbons. In: Bjorøy M, Albrencht C, Conford C et al (eds) Advances in organic geochemistry 1981. Wiley, New York, pp 504–512Google Scholar
  48. Radke M, Welte DH, Willsch H (1986) Maturity parameters based on aromatic hydrocarbons: influence of the organic matter type. Org Geochem 10:51–63CrossRefGoogle Scholar
  49. Rocha-Mello M, Telnaes N, Gaglianone PC et al (1988) Organic geochemical characterization of depositional paleoenviroments in Brazilian marginal basins. Org Geochem 13:31–46CrossRefGoogle Scholar
  50. Seifert WK, Moldowan JM (1986) Use of biological markers in petroleum exploration. In: Johns RB (ed) Methods in geochemistry and geophysics, vol 24. Elsevier, Amsterdam, pp 261–290Google Scholar
  51. Suárez M (2007) Geological framework of the pacific coast sedimentary basins, Western Colombia. Geol Colomb 32:47–62Google Scholar
  52. Tissot BP, Welte DH (1984) Petroleum formation and occurrence. Springer, New YorkCrossRefGoogle Scholar
  53. Tissot B, Califet-Debyser Y, Deroo G, Oudin JL (1971) Origin and evolution of hydrocarbons in early Toarcian shales, Paris Basin, France. Am Assoc Petrol Geol Bull 55:2177–2193Google Scholar
  54. van Aarssen BGK, de Leeuw JW (1999) On the identification and occurrence of oligomerized sesquiterpenoid compounds in the oil and sediments of Southeast Asia. Presented at 14th international meeting on organic geochemistry, September 18–22, ParisGoogle Scholar
  55. Wang HD (1993) A geochemical study of potential source rocks and crude oils in the Anadarko basin, Oklahoma. Ph.D. dissertation, University of OklahomaGoogle Scholar
  56. Zetaware, Inc. Source rock potential calculator. www.zetaware.com

Copyright information

© The Author(s) 2019

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  • J. E. Cortes
    • 1
    • 3
    • 5
    Email author
  • A. Mejía-Molina
    • 2
    • 6
  • C. A. Vargas
    • 3
  • S. I. Cortes
    • 4
  1. 1.Antek S.A. Geoscience Technology CenterBogotáColombia
  2. 2.National Hydrocarbon AgencyBogotáColombia
  3. 3.Universidad Nacional de ColombiaBogotáColombia
  4. 4.Geoscience DepartmentSouthern Methodist UniversityDallasUSA
  5. 5.Petromarkers, IncPearlandUSA
  6. 6.Yachay Tech UniversityUrcuquíEcuador

Personalised recommendations